Should I get a Power of Attorney for me and my son or redo guardianship for his medical treatments?

My 20 year old son received a TBI and was in PA for 7 months for medical treatment. During that time, his father and I got appointed co-guardians of estate and person. Our son successfully completed brain rehab and moved back home to me here in the DC area due to better medical facilities available for his ongoing care. His father is withholding most of my son's money from me stating that I am untrustworthy. My son is now competent enough to sign a POA. Most places around where I live will not recognize the guardianship since it is out of state any way. This thing has become a huge mess and is now very contentious. My son will live with me for the long term and is on my health insurance through my spouse as well as his own military health insurance and SSI/Disability/Medicaid. My funds are limited since he has control of all of them except the SSI/Disability check. He is not going to fund the legal battle between me and him. Any recommendations for attorneys in the area are appreciated.