I have some issues like that with my Harbron family. The kids were orphaned quite young & with the exception of the youngest, seemed to be quite out of touch with their family roots (the youngest lived until 97 & had some extra time to research when his daughter retired from teaching). What I've done is looked for every family tree (on ancestry, findmypast, myheritage) that mentions the family & has misinformation. I sent them a quick note & links to my extensive research with birth records, etc and a link to a page on wikitree where I'd covered one of their family members. I then asked if they could provide any personal stories so that I could add to their page, and if they're interested, to become the page owner. I think that being interested in improving their arm of the tree helps a bit & slowly it's been making a big difference. Some still choose not to make changes, for whatever reason. Regardless, there are more now with the correct info & they seem to show up first for people starting new trees.
I'm not sure if that's an approach that would work for you, but I thought I'd mention it.