I don't know about stretchskeleton, but for family funds, you need to enter it like so:
To add 100,000 Simoleons to the Smith family:
familyFunds Smith +100000
To subtract funds, just enter the amount with a minus sign.
If you have two families with the same surname, if you do this cheat from neighbourhood view, it might add it to the wrong one. I've had that happen and thought the cheat wasn't working. Meanwhile the other family were getting obscenely rich. LOL
ETA: I found
this thread about stretchskeleton