I'm sorry you're having problems.
It's really just about consistency. My dad's dogs are similar (well, one of them, really) because they're just not consistent and frankly don't really care to try and change them at this point.
But first off, don't worry about anything "alpha". Don't get a trainer who is going to come in and tell you to be all 'dominant' etc. The alpha theory has been debunked by the very people who created it years ago. Having well behaved dogs has nothing to do with you being more 'alpha dominant'.
My dads JRT mix Lilly will often be let outside by one of us, and I watch, 80% of the time she doesn't even go in the yard. Just stands on the porch. Then 5-10 mins later, someone comes by and opens a door for her, and she never even went. Thus, she comes back in the house and goes. I don't trust Jackson to go by himself either, so for our last potty of the night, I always walk out with him on a leash and say 'go potty' and make him go, so he won't wake me in the middle of the night having to go.
Since you say they sneak off like while you're laying on the couch watching TV, maybe (even if it's a PITA at first) try leashing them to you. If they try to get up, take them outside. Or if you don't wanna leash, the minute they hop off the couch, get them and take them outside. If they don't go outside, and you come back inside, leash them to you again. They will learn quickly. Just be 100% consistent for a full week, and see your progress.