#1 (not shown) Start SimPE. Tools->Neighborhood Browser. Choose your hood.
BACK UP. If you didn't back up,
BACK UP. Have you backed up yet? No?
BACK UP. If you haven't backed up, anything that happens is on you! I told you to
BACK UP! Open the hood.
#2 Click on SREL in the upper left window. Click on the header of the first column in the upper right window so they're in alphabetical order. Click "Plug-in View" on the tab at the very bottom of the window, if necessary.
#3 Scroll down to the name of the character you're interested in. Click it.
#4 Check and uncheck the boxes as appropriate.
In my example, I simply unchecked the "Family" box so that Chance could get romantic with his girl cousins. When he's made up his mind, I'll make the other cousin "family" again.
I know from experience that a married couple needs the following checked: Friends, Buddies, Crush, Known, Love, Married, Steady, Family.
Do not check Engaged, or they'll insist on taking vows again!
Do not use this method to create a polygamous family.
#5 (not shown) Click Commit.
Repeat steps 3-5 as necessary.
#6 Save.