Abusive ex into OSINT. Is VPN any use to protect myself against him seeing my online activity through my router?

As the title says.

I left an abusive ex who uses OSINT.

I should have seen the flags sooner as he never seemed interested in using OSINT for anything other than keeping tabs on people he didn’t like.

They wall drive(?) and have the details to mine and my families routers as we were together for several years. They claim to have hacked my families work machines in the past. I have informed everyone of this for their and my own safety.

I’m cutting them out of my life in any way I can but they keep appearing like a weed. I know they’re likely invading my privacy in more ways the the ones I’ve already caught them in.

Is a VPN any use to stop them seeing my online activity via my router, or do I just need to keep waiting for them to get bored and move on?

Thank you so much for any advice.