Warring in-laws

Hi all, so I'm worried about what's going to happen in the future.

My mum and dad are divorced and my mum has been with a new partner for about 10 years. He's an annoying personality and makes controversial statements to wind people up, but my mum is very happy and in love, so we just ignore the annoyances. They used to get on with my husband's parents, but ever since our wedding 3 years ago, when he was his usual annoying self, they refuse to speak to him and when they discuss him, they are clearly filled with hatrid, which me and husband believe is over the top. He hasn't intentionally hurt anyone, he's just rubs people up the wrong way. If on the rare occasion they're in the same room together, my in-laws pretend he isn't there. Now I'm pregnant, I'm dreading the hospital; it's going to be so awkward, with them in separate corners, refusing to look at him. At our child's future birthday parties, they're going to bring a hostile environment. We've tried talking to them, telling them to let it go, but they believe if they don't 'start trouble' then what they're doing is fine. He's not bothered that they don't like him, so isn't making the first move either.

Has anyone else deal with warring in-laws?

Thanks