Adult siblings living in separate households?

Hi... I am really struggling. I don't know if I'm being stupid here or what. Probably! But I'm stumped.

I'm trying to set up a nice cosy family saga in Henford-on-Bagley. I have four main families, who are all related. Basically, four siblings who all got married and went on to have their kids in the same little town. These close family relationships are really important to my storyline so I really need to set it up right.

This is such a vanilla idea that I thought it would be easy but apparently not!

I can't make everybody as one family in CAS and then split them up as it's way too many people. I've cheated the max Sim number to 80 with MCCC but that doesn't seem to work within CAS. It still won't let me go over 8. I did find another mod that supposedly helps with this but my game wouldn't load with it installed.

I tried having the siblings visit one another - with the aim of temporarily adding them to each other's household and editing the relationships like that - but I couldn't seem to find the option to do it, either through cheats or MCCC. I am admittedly not very expert at either but I've followed tutorials etc and it's not happening.

I've even tried deleting the siblings from their own families, making the four of them into one family, editing their relationships (all in CAS), then splitting them back out into separate households with their own families again... But when I did this I couldn't seem to re-link them to their spouses/kids. It gets locked out in CAS, and even when I use cheats, the right relationships aren't available. For example, an adult female sim (one of the siblings) has a young adult son... But when I separated and reunited them with each other, the only relationships on offer are married or engaged.

I'm getting really frustrated now 😬 this kind of thing shouldn't be this difficult! I know I could create them as kids, have them grow up, and then play out their romances/marriages/having kids etc, but that's not what I want for this. (I'm playing that storyline in a different save). For this one, I want the siblings to be middle aged and for the focus to be on their teen/young adult kids.

Surely, wanting to begin saves with grown up siblings living in different households isn't SUCH a niche idea that it should require multiple cheats, mods and mental gymnastics to achieve? I'm so stuck.

Hoping there's a really simple fix for this that I just don't know of because I'm a relative n00b. Can anyone help? Thank you!