Can you keep them in seperate, but adjoining, paddocks? After dealing with a possessive gelding, I would suggest keeping them apart from the beginning, it helps that your place is new to them... helps to enforce that they each have their own space - and as someone else said, strong stalls they can't knock down and solid runs.
If from the beginning you keep horse 1 in a stall with feed while working horse 2, they may get used to the separation without a battle.
When my mare started screaming for my gelding and ignoring me, I punished her by MOVING her feet while giving her the verbal warning OT OT OT! - if I was close I popped her nose with my lead shank EVERY TIME. She still loves my gelding, but doesn't dare call out for him - she knows it is a big time no no that results in lots of spinning circles and a sore lip. I would enforce the no screaming from the beginning.
Good luck with your adventure.