I have rwo indoor cats that i need to make into outdoor cats.
Welcome to the board. First, if you don't mind me asking, do you need to make them outdoor cats? You mentioned leaving them forever, that to me sounds like you are just going to boot them out and move away? It is very dangerous for cats to become outdoors after they have spent so long indoors, there are far too many dangers out there that they may not be able to defend themselves against. They could get hit by a car or killed by a coyote or other wild animal. I really hope you reconsider sending them outside, if it's because you are moving or allergic, you might want to consider re-homing them. Please please please think about this before you do it.
I agree with Cat - making them outdoor cats should be last resort.
Are they a specific breed of cat?
I think putting them outside should be your last resort.