Hi and welcome to YT.
I have indoor pad-trained dogs too and I will say, I don't think I'll ever do it again...I just think it's *very* confusing for the dog and that it's rare (although possible) to have a dog who will only go on the pad, and nowhere else ever.
First, it's important to understand that dogs don't pee in places bc of feeling "mad" at us (as you're suggesting above) - they don't pee to punish or out of revenge. So, I'd toss that idea out right off the bat.
As far as training them, I honestly don't know if there is much you can do since they are now 7 years old...and very entrenched in their learning of what's been accepted up until now. I can't even imagine getting rid of these 7 year old dogs...I think that would be just devastating mainly for them, but also for your family....not to mention it teaches your kids that animals are disposable, you know what I mean?
I wish you the best in whatever you decide, and I just hope these little ones don't get shuffled around to many homes while they go through this process...that would be tragic. Wish I had some brilliant idea for you, I truly do...but I just don't. I'm hoping others will come along with some wonderful ideas.
In the meantime, hang in there and don't give up.