Just because a person has a disability or long term illness does not mean they are on SSI. There's a difference between SSI and SSDI. SSI is "Supplemental Security Income." It is not Social Security however it is administrated under the Social Security Administration so it's very confusing. SSI is a form of Federalized welfare program as is Medicaid which is only for the most indigent.
SSDI is Social Security Disability Insurance and it is for those who have paid into it with their FICA taxes. A person on SSDI can own anything and can have an unlimited amount of money in the bank because they are not on welfare. Sometimes, a person gets both SSDI and SSI so "buyer" beware. The language is so troublesome, it can ruin the very lives its supposed to help. That's our system for ya.
If he has SSI or in combination with SSDI and is married, the TOTAL THEY can have in cash and material things is only $3,000. Check the SSA (Social Security Administration) to be certain. It may be that someone on SSI can "own" their own home if it is considered exempt. My advise is to encourage him to get off the SSI and make every effort to get back in the groove so he can stand on his feet. Take advantgage of every caree building opportunity there is for disbaled people if need be and above all,
TRUST YOUR INSTINCTS. The "fam" often treats their disabled members with disdain and/or takes advantage of them. Your son doesn't diserve that. Best wishes.