iphone contacts unwanted merge

My husband and I use family sharing and have done for years.

Today I got a phone call from his Dad but on my phone it said ‘Dad’. When I have always had him saved as his proper name. He’s not my dad! Now his mums has changed too.

Why have my contacts all changed and how do I put it bac? I’ve also noticed all his contacts are now in my phone. I’ve tried delete contact sharing in iPhone settings but they all stay there.

Extermely frustrating