How did y'all do it-- when you knew you were going for it, but it was a bit in the future, how did you maintain your cool?

This woman has made it nearly impossible for me to do so... keeps secrets about shit that affects our whole household, usually money shit, until she has no more ways/places to hide and [it] has to come out... just found out today, she okayed her father to buy a car for the 19 year old daughter in our house. Didn't say a word to me about it. Her husband. Kid's father.

19 year old supposedly has ADHD, and is regarded as 'too irresponsible'-- by her own mother-- to keep an eye on her siblings... is deemed responsible enough to operate a vehicle. Am I fucked up? Am I being irrational? I feel like I might be, that's why I'm posting here.

3 other minor children in the house, who I expressly FORBID to be in ANY vehicle driven by the 19 year old... the wife WILL defy that. It's definite. She does the exact opposite of practically everything I ask her, overturns what I tell my kids to do. Holy SHIT have I grown to despise this woman.

How. Do. Y'all. Keep. Your. COOL???

Edit: I searched the sub before posting, btw. Didn't see anything similar, sorry if repetitious.