How can I take Sims from a pre-existing save and start over entirely with a New Game?

[Tim Drake's Depression]

On the tin. I have a custom family that I wanna start a new game in a new save with. Problem is, for some reason they vanished from my Gallery. I checked every options that would enable them and nothing, so I have no idea where this one family went.

As of now, they have more than 8 Sims in the household and I need to delete the newer ones to save them to the gallery again but iirc, their sentiments and relationships will stay the same even if I start a new game. I do not want this, I want to fully start over

What's the proper method to do this?

Yes I could Google it, but I'd honestly prefer a few answers in one spot over scrounging around until I find one with a scenario close enough to mine.
(go easy on me if i sound stupid, im sick rn)

[Xenon The Noble]

<shift>+Click sim in household.
select "edit in cas"
In cas, select "save household".
The start a new game and pick that household. They'll have all the skills, and completed asperations as the saved household.
If you do it with MCCC, (MCCC->edit in cas) i know it saves stuff from mods, like that infamous WW mod that I totally don't ever use, which is pretty kewl since it takes a long time to set up attractions and traits in that mod that I never use.
Doesn't save info from Tripils's Sorcerer mod tho. Know that.

[Xenon The Noble]

One problem comes with the Death DLC. I picked one of my Elder sims to start a new game. Super powerful spell caster, done most everything and has all the reward traits that make a difference.
but the life goals thing doesn't take into account all the aperations he's already completed, so I gotta find stuff for him to complete, because death is coming.
Also, no family. Should have brought some family but the Denton47's household tool still can't do relationships between households.