adopting my sisters baby

Little background. My husband and I have been ttc for little over a year and 2 miscarriages. My sister has 2 little girls already and is pregnant with a 3rd due in about a month. She is in no condition what's so ever to take on another child. She has asked my husband and I to adopt her. What is the process? Any suggestions on where to start? Support for her and us? 
Someone told us it would be easier if she listed my husband as the father on birth certificate. Is this true? Does she have to sign away her rights? She is married but they are not together and the baby is possibly not even his. We don't know where to start or what to do and we don't have a lot of time.