I have noticed that lots of partners, wives, husbands complain about their partner's parents. These are the oldies who brought up their partners that they love.
The parents normally do not go out of their way to be horrible, they are probably normal people with lots of problems, personality traits, habits that offend etc. Nobody is "Perfect" everyone has things, sayings, ways of living that annoy, trouble, affect others.
Younger people need to learn to accept that nobody is perfect, including them, and stop criticising everyone else, thing, situation, viewpoints that they don't like.
Also, be more forgiving of their family, partner's family and neighbours.