The major problem with doing what your doing is that your doing it over and over again and you are getting the same results... Basically watch the move Groundhog day to see how that plays out... It isn't until you break the cycle that things are going to change.
We're training a new rat now, and every day is different... some days backwards and some forwards.. but that's fine as long as every day is at least slightly different we're making progress because we're influencing behavior through communication. And through trial and error and experimentation we're getting to know our new little baby.
To be perfectly honest, you have picked a hard row to hoe. Adopting rats from homes unknown can become a major problem... We once adopted a 3 week old rat from a feeder bin that had been brought in by a customer. She was beautiful and active and sharper looking than the other feeder type rats and she turned out to be part wild... man what a surprise! She could jump from my desk right into my face and lay a dozen mock bites on my nose before I could swat her off. And yes they were only mock bites and she didn't really hurt anybody seriously until she got much older. Even then, I only got bitten once and if handled with kit gloves by someone she liked, she was a real sweetheart. But I learned my lesson.
Now I can fix most screwed up rats, up to a point... I wrote the thread on immersion, but also keep in mind I have a 9 year old daughter to think about. Our part wild rat wasn't screwed up, she was just naturally vicious when provoked, which made her very predictable. And most of all she loved my daughter who could stuff her into doll clothes which made her safe for at least one of us...
The girls you adopted from the shelter may have been badly mistreated and have good reason to be afraid of hands and humans, this is going to take a lot of work to get over... Luckily they don't sound wild or part wild, if they were you would have a lot more trouble catching them and you would most likely have been bitten pretty badly by now, plus wild rats rarely do any damage to furniture, they prefer to be as unseen as much as possible... as in leave no footprints in the snow. There are a few other giveaways, but for the most part if they don't turn into a flying fur ball of fangs, claws and fur when provoked... you don't have one.
So change it up... naturally I'd recommend you read my thread on immersion.. basically start working with them in close quarters... send the message that you want to be friends and engage them... this is going to really stress them out big time at first, but with lots of engagement and patience and treats they are going to start to realize that you aren't about to drop them into a snake tank like their last owner did... An eventually their stress will subside and you will start to build your relationship with them... I realize it's going to get ugly before it will get better, but if your last relationship ended up in you getting hurt, you are going to be less trustful of the next one and the same is true of rats...
Remember things don't just get better with time, they get better with contact and work, time actually works against you as rats get used to the way things are and the longer it takes for things to change the less likely they will be to adapt to change.
I really don't want to discourage anyone from adopting from a shelter, or from anywhere, but when you adopt older rats that may have been mistreated or just not socialized, they come with luggage and sometimes with issues that will require lots of work. Going forward try and find rats from a known and if possible trusted source... When you can't do that, spend a little while with the rats you are about to adopt... The last six rats we adopted came home with us without a box or cage... The only rat we ever took home in a box was our wild child and that's only because the girl at the store insisted, after telling us how sweet she was and what a good home she came from... (like she didn't know what she was selling us and why she was in a feeder bin). Oddly, although I'd check my homeowners and medical insurance first, I might adopt another baby wild rat, they are truly amazing animals... BUT, I'd never adopt any rat that I couldn't easily handle at the point of adoption; domestic or wild type. It's not that I can't fix them, but with so many sweet little ratties out there in dire need loving homes why would I want to bring home one that's already screwed up by someone else.
As your already committed, I encourage you to read my immersion thread and keep in mind many of us have worked with way funkier rats than you seem to be talking about and most of the time things worked out really well for everyone. The vast majority of rats can build a meaningful relationship with their humans and just about all of them can be substantially improved. You really did a nice thing by adopting rats with issues, but expect your commitment to be tested as you proceed from here forward.
I've worked with a very few select folks who actually adopt screwed up rats on purpose to rehabilitate them... some get really good at it. But they all tell me that once they build a bond of love and trust with a screwed up, problem rat, the relationship they built is worth every drop of blood, sweat and tears it took to get there.