What is the best way..

My mother in law has been begging me for another baby (which is what we wanted) i am 5weeks pregnant today, I'm thinking about telling them when I'm 11weeks with a sonogram picture, but I'm nervous about my father in law, he shows no emotion. Me and my husband have 2 kids together right now, and my sister in law has 2 also. Am i over thinking this...but i think my father in law is going to feel overly overwhelmed and im scared for his reaction in a few weeks. What's the best way to tell And haul butt at the same time lol?