Removing iTunes accounts from previous employees

I took over the phone manager position about a year ago and discovered an issue that had been pushed to the side and I would like to correct it. I have several (30+) iPhone 6s that I cant get rid of because the user created non-standard accounts and I can't wipe them. Most of the users are not with the organization anymore so I can't reach out to them to provide the information. I can remove the organizations management, remove the screen lock but can't disassociate the Apple ID. Is there any way to do this that isn't jailbreaking or paying a 3rd party vender? I'd like to donate the phones to a local battered women's organization but I can't without wiping them. Only other option I can think of disposing of them is physical destruction but that seems wasteful.

I'd like to figure this process out since were likely to be updating our current phones (Xr) within the next year and I know we will have a few more locked devices to add to the pile.

We've since changed our policies to where we set up the apple ID instead of the user.