If a babysitter did this, you would fire him or her. If my husband had done this, I would have taken all the laptops and game devices with me when leaving the house. I would also have had a talk with his mom and dad about his and his brother's behavior with the baby. I'd tell the entire family, I would be so angry.
I guess you can tell I'm not above embarrassing someone when I'm THIS angry.
You don't leave a baby in a highchair for six hours.
Why is this couple still living with you? What is your SIL doing?
You say he's a wonderful loving husband. What is loving and wonderful about a husband who sits gazing at the TV ignoring you and his daughter? It sounds like his bro and the TV take the place of YOU. You have talked about it til you're blue in the face and it hasn't done a bit of good.
Instead of expecting your husband to tell his brother to leave, YOU should do it. I swear, I'd have a fit if it were me. Don't mince words - tell your BIL and SIL to go find somewhere else to live. They are ruining your marriage and being party to your husband being a very poor father.
It's time to take back your house and if it messes your relationship up with your husband's family, too bad.
That's my opinion.
Dawn