I think, as long as they are not both males, you can leave them together.
I keep a display tank in my living room, and I rotate different snakes in and out for show. I will sometimes keep two large females or even several juvies (regardless of sex) in the tank and they are fine. They curl up together and seem to enjoy each others company. In the wild several may live in the same hole, even with different species of snakes I beleive.
Spreading a disease between them is always a concern, but if you keep the cage clean and the temps right, you should be fine.
There is risk in everything in life, enjoy your snakes.
Also, I would run one undertank heater regulated to 80 degrees off to one side of the tank then run a spot for basking during the daytime. In a large tank you may need additional night and/ or daytime bulb, you have to play around with it.
I have had bulbs blow out during the night and I have been thankful that the undertank heater kept them warm enough through the cold night, so its like having a back up heat source.
In a large tank like your talking about, I would put a couple hides in the hot and cold ends, or I like to use a large piece of driftwood for them to hide under. The larger snakes arent as skiddish about hiding once they are used to things.
Enjoy your snakes - treat them well.
Alan