A relative is, infact, able to take your SSI from you, however, this only can happen if they get approved as your Representative Payee. Unfortunately, that is extremely easy to do. They just have to show that you spend your SSI on alcohol.
Here's a resource on this:
http://www.disabilitysecrets.com/re...bility/ssdi/payments-representative-payee.htm
Basically, they can call the SSA and rat you out and offer to take over management of your funds. In the case of alcohol, SSA will most likely grant the request. Its not a very difficult process at all.
All they have to do to get the ball rolling on this is call the number here:
http://www.ssa.gov/payee/
With that said, the money is still yours, but you won't be the one deciding what its spent on anymore. Every single transaction is logged in detail. They can't use the money for themselves but they control what it gets spent on otherwise.
By the way, you might want to save yourself the headache and stop drinking. If they follow through with their threat and call SSA and get the ball rolling on this, you will likely end up with a payee, whether it be them or someone that SSA appoints (you can also have a friend take over, you do still have a say in it although SSA has the final say in the matter). If this happens, in order to get your payments back to yourself you have to prove that you're now capable of managing your own finances. In doing that, you can shoot yourself in the foot and lose your benefits because they consider your improvement to be great enough that you can go to work.