I have list of ids and need to load the objects.
Is it preferable to use IN or load them as separate objects using get by Id?
Or is there any other efficient way?

Any suggestions would be helpful

IN is definitely a better way since Hibernate will pick all the objects up in one go. 'get' will hit the DB one by one hitting performance.

If you want to load some object to set into the many-to-one relationship,
you can use load instead of get