Breaking Engagement News To An Anti Marriage Parent?

My partner recently proposed to me on the 9th of April this year, but my parent and their partner are heavily anti marriage

Basically they say "I don't care about marriage but it's a mistake, it's a waste of money, it is doomed to fail, the woman changes when she signs the marriage documents or gets a ring on her finger, the guys become fat and lazy, etc"

We've told his family and even got the approval which I wanted, but now I don't know how to tell my side... It's the best news ever and I can't tell them... And I really I want to!

But neither him or I know how to bring it up to them... Someone please help, any advice is appreciated

TLDR: Anti marriage parent and their partner are heavily anti marriage to the point of condemning it, I'm now engaged and haven't told them yet... help? Any advice?
Breaking Engagement News To An Anti Marriage Parent?
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