I’m struggling- vent session

I have an almost 4 week old (FTM) and she is not sleeping well at nights. Is usually up from 10/11-3:00 am. Not necessarily crying, but just fussy and wide awake. I could deal with the whole “sleep when the baby sleeps” but now my step son (4) is here for two weeks and I am REALLY struggling. My husband works, so I’m up all night with a newborn that doesn’t sleep and a 4 year old that is awake all day. On top of that, my step son is waking up every few hours for stupid shit and guess who is getting up with him... me. I try to let my husband sleep since he has to work, but I’m really starting to resent him and his son (I know it’s not his sons fault) but I didn’t want his son here so close to my due date but my husband only sees his son 2-3 times a year (16 hour distance) and I know the time is important. But I feel like I am losing my mind and so sleep deprived.