Hello everyone!

I'm having a little problem that I haven't been able to solve, since Sims 4 is still semi new to me. The thing is; back in Sims 2, you could easily create one family (parents and kids) and then you remember that you'd like to add grandparents to the family, but you want them to live in a separate lot. So, you create grandparents and move them on a different lot, then you open SimPE; where you edit relationships, save it and in-game it works. Grandparents are indeed connected to the original family.
I haven't been able to figure this out in Sims 4. I don't feel like using command lines and such.
Any solutions?

The way to achieve that in TS4, is to first have the older sims you wish to be grandparents stored/saved to you Library.

The younger sim family who already live in game, take them into Cas.

While in Cas, hit your Library tab and select the stored older sims to add them to family.

Then select the Relationship options and set them as parents of the adults, which it turn automatically sets children as grandchildren. Save and return to game. One big happily related family, then finally move grandparents out to their own home.

The one annoying rule you have to abide by while doing this relationship altering, is that the new additions to the family (in this instance the grandparents) always, always, always have to come in from your Library first.

You cannot do this biologically-related trick with two sim families who already exist in your world. Existing sims have been set in stone as non-biologically related and it will fail. But via Cas and a merge from the Library, that'll do the trick for you.

Thank you for the answer! Much appreciated. I shall do this.
I'll have to remember this info. As I said, in TS2, this thing was much easier and it always worked. TS4 did improve a lot, but some things are just messy. I don't know why EA felt the need to fix something that wasn't broken, but whatever.

Thanks again. :D