Can't delete photos in text messages.

I'm trying to free up space on my iPhone 11 125gb. One of the worst space offenders is photos sent and received in my text messages. One thread in particular, my wife and I send thousands of worthless photos (i.e is this the right coffee creamer) but also photos and videos of our kids I want to keep.

I have tried- opening the text chain, selecting the contact at the top, scrolling to photo, select "see all", then hit "select" again so that i can go through and delete certain ones and keep others. I try to select several dozen at a time to delete because every time I start over i have to scroll to find where I left off. However this either doesn't delete the photos or the photos reappear the next time i open the text chain. Are they being recovered from some kind of iCloud sync?

I have also tried deleting them through system Settings-iPhone storage-Messages then selecting either "photos" or "review large attachments". neither of those work as well, additionally that method doesn't let you select a particular thread.

Any way around this other than scrolling the thread and deleting photos one by one?