Taking responsibility for an illegal whose been caught at the border.

[Thisisfate]

My boyfriends brother is from Ecuador and got caught trying to enter America through the desert. He has been arrested and waits in an immigration jail. My boyfriend and his other brother who lives in the united states illegally, have hired a lawyer to help get him out of jail and legally into America. The lawyer suggested that a legal us citizen sign papers taking responsibility for his brother to better his chances of being released in America. Because I'm legal they want me to sign these papers taking responsibility but I dont know what that entails. The lawyer working for him is based out of Texas and I reside in Boston so I don't know where or who to ask. I know that it's possible for an illegal immigrant who has even caught to be granted access ino the united states as for my boyfriend just got his brother in law entry with the help of a lawyer. But I don't want to jeopardize my life and put it on the line if it could effect me in a negative way. I don't want to have legal trouble for helping out.
Has anyone ever heard of signing responsibility for an immigrant, or know the procedure or the consequences?
Any information would be helpful.