No, you aren't torturing your cats, and it's logical to keep them in if there's traffic and coyotes outside. However, indoor cats do need more stimulation and play than outdoor cats. You'll need to set aside time to play with them and maybe do some "catification" in the house to give them lots of high places to climb to. The Jackson Galaxy books have some great idea in them, I highly recommend them.
If possible, consider a harness and leash and taking them out for supervised exploration. It's a way for a cat to experience outdoors without risk of being run over or eaten by predators. Not all cats take to it, but starting with maybe five minutes of outside time and working up might get them started. I'll be honest, when they do take to it they might pester you constantly to be taken out, but you can ignore it if you've done it once already in a day.
Oh, and clip their claws so that they can't hurt each other when they do play fight.