High child support payments

My son has two children 3 years old from 2 different women and is paying $500 from each check ($1,000) a month. He has custody of his 13 year old daughter. He has a 1 bedroom apartment which he can barely afford now and his car which he can't afford anymore and his daughter whom me (his mother who is living off my disability) had to by her school clothes and supplies....My son is ready to lose his apartment now because of his child support. It's either his car or apartment...which one should he keep???