Is it ok to put my friends before my family? ?

It is always sad to hear of such selfish parents. First, he is your Mother's husband not your Step dad. My suggestion, if you are going to be in town for seven days, or longer, invite your Mother and sister to meet you, your baby and your girlfriend for lunch. Make it very clear to Mom that her husband is not invited. Visit with your Mom only in a public place. If you are there for less than a week you really don't have a lot of time to visit with everyone other than your friends. I do hope your sister can visit you often at your friends houses, that she is safe and can find a better life soon. Under no cirstance should you go to your Mom's house! You have no idea what you may be walking into...