I need some help with the parents in my sims house and artist's emotions please

Mending their romantic relationship will just take patience. If their friendly relationship isn't fully green yet, just focus on that until it is. Then take it slow with the romance. Start with flirting, then complimenting. But don't go too far or overdo it; just take it slow.

As for how to change their emotions, that's actually pretty easy. There are a ton of different ways to influence the emotions your Sims are feeling, one of them being items you can buy from Build/Buy. I know different packs also offer ways as well, like potions and such.