What if someone is forcing you to sign over your rights on your house?

My mother and I bought a house in 2005, she didn't have enough income, I didn't have good enough credit, so it worked out better this way. In 2009 I moved out of the house and in with my fiance but my mother continues to live in the house til this day. My mother applied for a grant to help with repairs I got a phone call where a couple of my siblings are wanting me to sign away my rights to the home (apparently my mother can't get the grant because I am still on the deed). They said that my name is no longer on the mortgage but was still on the deed. What I don't know is how did they get my name off of the mortgage with me not signing anything? Can my mother get my name off the mortgage without my signing or did someone forge my signature? What can I do if someone did forge my name?