Really I'm looking for clarification on how the rule against "content made by another" works irt works made by two or more people. Right now a friend and I making a custom neighborhood in the Sims 2, it was my idea and I was originally just gonna do it all myself but the friend is a better builder than me so I asked her if she'd be interested in building the lots for the hood and she said yes, so now it's become a collaborative work where she's building all the lots and I'm doing pretty much everything else such as decorating the hood, making all the sims, writing all the biographies and such for the hood, editing the skills, careers, memories, etc. of the sims, stuff like that. And it's not like we're doing all this completely independently of each other either, like it's very much collaborative, like I'll tell her any specific things I may want in a given lot and as she builds she'll show me the lot and ask for any feedback from me, and whenever I get new ideas for the hood I'll bounce them off her and see what she thinks, stuff like that. Really what I just wanna know is like would it be fine for me to upload the neighborhood myself, while of course making sure to credit her for her contributions? Should I instead have her create an account and upload it while crediting me for my own contributions, since building the lots is probably the most intensive part of making a custom hood? Should we do some other third thing? Would love some clarification here.

You can both create an account, then apply to the admins to create a group account also. For example, if you look at this user account, you see that they are also in a collaboration with three groups, and that they have creations with those groups.
https://modthesims.info/member.php?u=4407

I see. So I should have her make an account too, and then we make a group account, and use that to upload the neighborhood to the website?

Yes, that would be the way where you both are represented here.

If, say, one of you didn't want to make an account, you can also chose the other option that only one person uploads. The only thing that matters in the end is, what do you two agree on? What do both of you feel comfortable with? So only one can upload and just tell about the collaboration and credit the other creator appropriately if that's fine for both of you.

I am part of a lot of collaborations too, and we used all sorts of uploading methods: only one uploads with proper credit, making on own website for it, or making a group account here and have a shared upload.

All right, good to know, I'll talk to her and see what she wants to do.