Beautiful Relationship

I'm 27 married 2+ children, I married when I was 23 and married my boss's daughter and everything is perfect. My wife is a stay-at-home mother 25, and we live across the street from her parents. Nothing out of the ordinary in that. Her mother is 51 and her father 63 and he seemed to lose his sex drive and started playing golf and not fucking his wife all that much. My wife really loves her mother, and she asked me to take up the slack so to speak and fuck her mother. To say I was shocked would be an understatement, but I was shocked. But agreed to please my wife, but I couldn't get aroused with her mother by myself and so threesomes became our sexual preference to both satisfy her mother and allow me to perform. Which is about 3 times a month and has resulted in my wife getting pregnant again. Which will mean we've a 3year old, 1year old and a newborn when our new daughter arrives in about 6 or 7 weeks. My father-in-law thinks we're having the children too close together and maybe have too many if we aren't careful in future. We are very happy with how things are proceeding and I'm able to fuck my mother-in-law (MIL) only at the moment, but my wife needs to be in the bed with us. But she isn't as active before she got pregnant.