There are several ways around some of the challenges you have created for yourself.
First, if you don't have any other Sims on vacation other than the ones who are stuck in limbo or even in the vacation hood, you can simply delete the vacation world (within the game) and the Sims should return back to their home lot. You can add the same world again if it isn't a custom world you were using for a vacation hood.
Second, if you don't want to go through the fuss of marrying off Sims you can use the headstone to make Sims become involved with other Sims on a lot. (cheat). Choices on the Headstone can help relationships and spawn kids etc.
As far as having six grandchildren, no one has to go through the romance to do that, simply adopt. LTW filled.
If it's too much of a chore to tend to those six, you can always move them out with another Sim and put them in a house (so your Sims can call them) or buy them each a cellphone, and or leave them in the bin, and never play them again. You can age up Sims with the Simmodder cheat object in the game. Or play them later, one by one by adding a Sim you don't care about to household and have them move out with all or each one at a time. Easier to play one by one.
Crashing, it sounds like you don't have the game set with Graphics Rule Maker correctly to where it won't crash, and will use the right amount of memory to keep it running if it's setup correctly.
Things that use too much memory in The Sims 2.
Walls, walls use a lot of performance power for this game. It's why a vacant lot is much smoother.
Inventory, for every townie in the hoods. If Sims visit owned businesses and your Sims sell them stuff every day, they are loaded down with stuff in their inventories.
Memories, every time you see Sims on community lots there are more memories being generated for every Sim there.
That's just a few things let alone how many Sims and visitors are on a lot.
It's why the Graphics Rule maker must be set to read the correct amount of RAM and memory on your video card.
University, there used to be a mod that sets the week for each semester to 3 days or maybe even 2 days. No one says they have to pass...lol.
I think I got it at Mod the Sims years ago but can't remember the name of it. But 3 days was enough for most of them to make the Dean's list in my game so that mod was very useful to shorten their time at college.
