I would think that Merge Replication is the way to go for you, because with Transactional and Snapshot replication, the subscriber cannot make changes to the data.
Looking at your post, I think merge replication is the only option, because you want the subscribers to be able to enter data locally and then have that data...
Changing the IP address should make no difference. Replication relies on the machine name not the IP address. So if the name has not changed you should not have...