I'm looking to create a group of sims with each their own lifestyle.

Chef , learn all the cooking and baking skills

Your group looks good, it'll be fun to play!

I'd break up the artist into one sim focussing on visual arts and crafts and another one who specializes in comedy, acting and dancing. If you want to add an athlete, consider a cheerleader. They can cover some of the dancing/singing/acting aspects.

What about the new fashion photography career? Maybe enhance it with the Get Famous media production skill where your Sim takes photography via her or his fashion photography career and suplimenting it by creating video recording and maybe becoming a famous influencer?

Party boy - someone who is a mixologist, the dance machine, non- committal, and insider traits would all fit the profile. He could be a player who woohoos a lot and goes to bars and pop up party invites.

Domestic crafts? Gardening (which has some crossover with the survivalist), cooking (homestyle, gourmet, and baking), handiness, and, if you're planning on having kids around, parenting. Just for the sake of not fitting a stereotype, could be a rough-looking guy. Both they and the survivalist would be pretty practical, but the survivalist would be happy in a tent and campfire, whereas the domestic one would especially love having a nice, comfortable space around them.

I do also agree with @EnkiSchmidt in splitting the artist one in two - one performer (comedy and acting especially), one artisan (painting, woodwork, et cetera). Music could fall into both categories - maybe something like violin for the artisan and DJ mixing for the performer? Alternatively, the artisan one could be combined with domestic (making a nice place to be), and the performer could work with the partier that @sunblond suggested. So comedy, acting, DJ mixing, mixology, dancing, and charisma.

So far, I'm liking the look of:

Scientist: Genius, and Geek, Loner, and Perfectionist would work as well. Main skills are logic, rocket science, programming, and handiness.

Mage: Not sure about traits. Main skills are... magic, obviously, but gardening would also be useful. This one does seem less well-developed than others and could be folded into another. Survivalist mage? Domestic mage?

Hacker: Geek for sure. Main skills are programming, video games, logic, mischief, and media.

Survivalist: Loves Outdoors is a must! Loner could also work. Main skills are gardening, fitness, swimming, fishing, herbalism, there's a lot that could fit in here.

Domestics: Foodie, maybe? Creative, Neat, Family-Oriented (if raising kids). Main skills - homestyle and gourmet cooking, baking, handiness, maybe parenting. For the arty side, painting, woodwork, maybe an instrument like violin. Gardening, as crossover with the survivalist.

Partier: As sunblond suggested, Dance Machine, Insider, and Non-Commital. Mixology, dancing, acting, comedy, charisma, DJ mixing.

Over-achiever mom. Max out cooking skills, make gourmet meals, learn how to make exotic dishes. Work on parenting skills, help with homework. Always dress the kids just right for the occasion. Obsessed with taking and hanging photos of their family. Has lots of play dates with other parents. Lots of family time, like going to the park or going on family vacations. Have their kids in various clubs. Everything for this sim would revolve around kids and family.

Party goer might indeed have enough to offer with mixology, charisma, comedy and such. Maybe that one could take some skills from the artisan. DJ skill might fit this sim more after all.

Probably won't be a sim focused on family if the household ends up being eight people since I plan to keep the group together for quite a while, I play with aging off. I like letting sims pick their partners on their own so I'll see who they click best with in this group of unrelated adults.
Some will probably learn some cooking on their own, I feel it's not enough of a lifestyle.

Fashion photography could work, but might be high maintenance, having to take all those pictures and not much else to do than that single skill to develop which requires my constant involvement.

I think you need one

Disappointment - watches tv,plays video games, read many many books, biggest goal in life is to eat lots of food , maybe own pets, probably bit of a loner maybe bit gloomy

not allowed to have a job but can make money by stealing things or lending from other sims or selling stuff or odd jobs whatever but always unemployed

(i just felt this group of sims is unrealistically successful so idk i just need to represent the disappointment TM)

That could work. I've also considered an evil vampire.

The plan is to have all these sims be in their late teens, just finished college and starting their lives. All living together, likely everyone sharing a room with someone. And as they advance in their goals, I update their looks to look less like teenagers and more adult. But initially they look like they are in college.

Who I have so far:

-Scientist.
He's a boring fellow. He's a genius, neat and a perfectionist. Wears boring clothes, socks in sandals for example. Not the type of geek who'll want to talk for hours about their favorite videogame, but the kind who'd talk for hours about scientific facts no one cares about. He's Indian.

-Hacker.
She's a geek, cheerful and a goofball. African American, colorful clothes, glasses and a cap. Very interested in all modern tech stuff, will be using social media.

-Survivalist.
She loves the outdoors, is paranoid and a loner. She wants to commit to gardening, fishing and wants to explore archiological sites. She'd probably be the kind to wrestle a bear if he takes her flashlight or something. If there's ever a zombie apocalypse, she'd be prepared.

-Artisan.
He's an Irish guy who kind of tries to live up to his celtic roots of bards and storytellers. He wants to paint, sing, play instruments, perform and pretty much be a modern bard. He has the creative, art lover and music lover traits.

-Mage.
She's a good student with the creative, perfectionist and bookworm traits. But her journey through magic might change her as she'd test out all kinds of potions and spells.

-Jock.
He is athletic, hot headed and a bro. He'll want to reach his athletic peak and might try for sports, but he might switch over to secret agent or detective later on to get a more interesting career and lifestyle.

-Business man.
He's materialistic, ambitious and a snob. He wants to climb that corporate ladder and earn lots of money.


So there's one possible slot left that could be filled with an interesting woman.

I've considered a party sim there but feel it might be too high maintenance having to constantly throw parties. But it's still an option.
An evil vampire too, posing as a friendly looking woman but being rotten to the core with a hideous dark form.
A lazy slob could work too, but sadly even lazy slobs tend to be pretty active in this game. But it might be an idea to just have this sim do their thing and never give them any orders at all, just to see what she'll do. I did have someone like that in my last household, she became an internet celeberty after a while.

Still, someone evil or lazy could stir things up in the household, making things harder for the others. But then it might just be about creating the worst roommate ever with the traits that will affect the others most negatively.
Clumbsy seems good to break stuff, mean spirited might work better than evil to create conflict. And a slob to make a mess.

But another productive sim could work too, if they can be given a nice unique range of stuff to do to keep them busy. Perhaps a less likely combination of traits or such.. Wanting to romance on it's own isn't enough for example, that would need to be expanded with other stuff.

Go for the evil Vampire. Always go for the evil Vampire.