Two cats that fight and attack each other for past two years

I am looking for advice on training my two cats to get along. They are both rescues. The 4yr old is a Tortoiseshell female and the 2yr old is a Bengal male. We keep them separated when we are not at home and at night. They are fighting less then they used to, but if she is asleep, he just has to jump on her and start a fight, and then she gets even for a week chasing him into his carrier and screaming in his face. I'd like to be able to let them both outside during the day together without having to worry that one of them will attack the other--particularly in one of my non-cat-tolerant neighbor's yards. We have cat carriers set up as safety zones to retreat to--she also uses it as a place to sleep. Right now, they take turns going outside each day and the one inside haunts the windows waiting to see the other one so they can switch places. Both like to play with toys. This has been going on for two years now. How do I double clicker train them so both will respond at the same time? Thanks.