You could try saving all your games (ie, neighborhoods) to a DVD or flash drive, then uninstall some of your EP/SPs and playing a reduced game for a while.   That would also entail removing certain custom content, which would help, or removing all current cc and saving that to a DVD too, and starting from scratch, maybe just Maxis recolours and whatever mods are necessary for the latest EP you have in the new install.

This is probably a dumb idea spawned by being overtired, but you could set Marilyn's relationship to Mary-Sue and leave Mary-Sue's relationship to Marilyn alone.  Just edit the SREL(I think) resources without changing the neighborhood relationship table.

BTW, I do have a group marriage that works reasonably well if you remember to turn off jealousy or use Cyjon's jealousy hack.  I set it up by having 2 couples get married, then making all 4 married to each other by editting their SRELs without changing the neighborhood relationship table. 

The reason you cannot have one person married to 2 others in the neighborhood relationship table is because the game will crash on save when it tries to figure out the married couples to place them together when generating the family splash page.

As far as I'm aware, neither the game itself, nor the only known extensive-enough editor (SimPE) are capable of handling more than one pair of parents per sim.

And before anyone asks... Equally, it's impossible for any sim to have more than one spouse and the game treating them both equally.

EA'S employees' imagination never stretched that far.

Hi guys, played Sims 2 for nine years and I have every mod/piece of CC going... but I need help!!

I've just reset my Pleasantview, and have created an elderly couple (Victor & Marilyn), their daughter Sophie, and her son, Parker.

Anyway, my plan is to introduce Marilyn as Mary-Sue's birth mother, therefore making Victor her step-father, Sophie her half-sister and Parker her nephew.

However, using SimPE - how can I do this without removing Herb and Coral as her adoptive parents on the family tree?!

Yes gummilutt that is the one I have been using ever since I got M&G. I have never had any problems with it.