that is an extremely difficult situation....but you can't MAKE him be sober, stay sober or even WANT to be sober. he is after all 30 years old. Repeatedly sticking him back in rehab isn't working and is a waste on many levels, financial, emotional, even the other sobriety seeking clients at the rehab.
one thing that droppping him off at a homeless shelter does is purely FOR YOU....gets him out of your house, so you aren't housing and supporting someone whose main goal is to get highly intoxicated. while he has the right to drink and to drink himself into a coma if he's a mind to, he does not have the right to violate your home, your rules and your sanity to do so.
about the only drastic option would be an involuntary committment, but even that may not have the desired outcome.
i really feel for you guys, all of you.