NTJ If you need to get more assertive, start with your wife. She deliberately spilled wine on the boss's wife because she was jealous. That's petty and is sure to continue AND escalate. Her behavior is going to end your job. Make that plain to her.
NTJ You shouldn't have to give her an extravagant gift to "repair the relationship." Don't give in. It will not be just one time. Also, giving in would be rewarding her for abusive behavior. She is basically blackmailing you. It really doesn't sound like she has accepted you all as family.
Plain and simple - you have already entered into an agreement to rent the duplex to your brother and BIL. You are now their landlord. You must abide by the agreement even if it was just a verbal one. NTJ