It looks like your son, his wife and 2 kids have been living with your for 4-5 years, now. Under the very best of circumstances, this is not a healthy arrangement for anyone. It sounds like all it's accomplished is mutual dependence and keeps your son a perpetual adult child.
Know that your home is not their only option and the longer they continue to live there, the more challenging it will be for anyone to achieve some semblance of normal.