Hi, sorry I only just saw this.
I am not sure this is even legal if they are being bought/sold.
If they are pets then you can fly them in Europe but you will need to comply with all the regulations which you will need to speak to your vet about.
Could you give anymore detail?
It is worth noting that transport is probably THE most stressful thing an animal can go through, so if it can be avoided all the better.
Zo