Ownership of both pigs and land are irrelevant.
All that the authorities want is who is responsible and that they adhere to the law.
Therefore you can have land registered to you under the CPH rules which you do not own or even rent - as long as you are the responsible person.
Similarly any animals going to a CPH are the responsibility of the CPH holder, irrespective of ownership.
That's the way the system works.
You can have multiple pieces of land registered to your CPH as longs as they are within 5 miles of each other, and these can be treated as a single holding for movement purposes. You can do this quite happily, but generally we do not recommend it, as whilst it allows you to freely move animals between these parcels of land, it also means that if any part of your land gets subject to say F&M restrictions, then all of it does, and a cull would be against all the bits, not just one. However I digress.
As you have said the land is 10 miles away, then 2 possibilities below
1. You can register their land against your name, but it will have a separate CPH, and movements will be treated as moving between holdings, with standstills etc. This would mean that any pigs coming back will put you on a standstill, even against themselves, so you could not bring them back to your place prior to slaughter unless there is a 20 day period in between, so they’d need to go straight from the new place to the abattoir. For e-aml, you’ll simply have another CPH, and set up movements between the two, being both sender and receiver.
2. Alternately they register as the CPH holder, in which case they’ll need to register with e-aml as well, and you’d treat moves as farm to farm etc.
As I said, the authorities care not one iota as to who owns the pigs, so whether you sell/transfer ownership is up to you.
OK so that’s the rules, is it a good idea? I’d feel uneasy about having a CPH against my name where a novice was looking after my pigs, - any issues and it’s me that’ll get it.
If they have a CPH against their name then they’d be done for infringements of the rules, but I’d look at it that it’s still my pigs that I’m trusting someone else to look after!
Overall I think your plan to sell them weaners and stick at that is the best course !