Existing user accounts LDAP integration

Question

I currently have a few machines in my house, including a Windows PC, a MacOS laptop, a couple of RPIs, a Synology NAS and a small server. I would like to start using some form of centralized system (e.g. FreeIPA or even remote options like JumpCloud) to avoid having to manage accounts locally and mainly, to use NFS properly. This would run in a docker swarm composed of the server and the RPIs if that has an impact. The problem, however, is that all these machines have already local users.

Is it possible to "migrate" or "merge" local users to LDAP users easily? I would like to avoid changing UIDs if possible, all linux machines have users with identical UID and GID for the users I want shared (not system users or groups), but the MacOS machine user has a different UID (and group, e.g. user:staff instead of user:user) which could be an issue.

In case the Windows machine would pose a challenge I would be fine skipping merging that account as long as I have a way to use NFS on it.

Thank you.