1). Give them no money.

2). Don't sell them your car at half price.

3). Cut the apron strings.

These "kids" are now adults. It's time for tough love. Part of being an adult is learning how to live within a budget. If your SS didn't have that car/whatever, they could probably easily afford 2 used cars. Don't sell them your car for half the value. This is called enabling. You would be helping them be dysfunctional.

If you don't let them learn the hard way, they will never learn. This may include debt, bankruptcy and such, but again, they are adults.

The kids mom helped create this problem. Tell her tough, it's not your job to bail them out. If they are living above their means, it's time for them to crack down, get a cheaper car, get a cheaper apartment and eat ramen.