My kids 9&7 & I have had flu since Sunday night and started tamiflu (oseltamivir) Mon night. Are we still contagious on Friday. I don't want my 4monthold sick.

You all still may be. contagious. Tamiflu (oseltamivir) can shorten the course of the illness symptoms, but your respiratory secretions probably still have some infectious particles. I would still try to keep your other children away from the baby at least until all symptoms are totally gone for 24 hours...and for you and them, good hand washing. Ideally if you have an option of someone else doing the care for the baby, also do that.