HONEST OPINIONS NEEDED!

I have a 7 year old son who has his dads last name and my surname as his middle name. I am now getting married and expecting my second child but I am worrying over naming him/her. I am worried about myself, my soon to be husband and new baby all sharing a last name and then my son not having it, changing his name is not an option, although his dad takes very little part in his life. I was thinking I could also give the new baby my surname as their middle name so they both share that- but is it weird for two kids to have the same middle name?