Rats are stubborn,, but I tend to be even moreso... I tend to get my way, so I personally would persist. I had good early success with intros and thought myself quite adept at once. Then things that worked once, didn't the next time... I've had two intros that ended with long brawls under the photocopier when they got away from me.. They went completely out of my control and 45 minutes later there was peace and both rats were cuddled up with each other exhausted.
I've done intros in my immersion space, that were over in less than 5 minutes and I've taken stubborn rats to my 40 acre safe site where they shouldn't fight over territory and sometimes it went well and sometimes I brought home wounded rats... because one rat learned to use tree branches to pounce on the other. I did the intro with my part wild rat in my lap on an easy chair and that went pretty well and I've gotten bitten by the new little rat I was protecting from the larger older one. I could write a novel about things that worked a treat and then didn't the next time I tried them. And yes, I have come up with a few general rules... like intros require that both rats be able to defend themselves so one doesn't just stomp the other. But a smaller faster more agile rat can do pretty well against an older slower rat for instance. I still prefer to start out hands on, but when that doesn't work I give the rats lots of space and step out of the mix... All in all, I play it by ear.
Still, in general when your rats are all socialized to see you as the parent they will build a social structure around your guidance. The outcome is almost inevitable despite however lumpy the process gets. In the end, rats are practically designed to build social relationships and live in orderly societies. So far, at least I've always been successful in the end.
But yes, things can and do go wrong... rats can get injured or even killed in the process. It's very uncommon, but it happens.
So last week we adopted Misty and Cloud has already gotten at her twice, once she yanked her out of my hand and tried to run off with her and once she pounced on her when my daughter left Misty in Cloud's cage and not realizing Misty was in the cage I put Cloud in... both times were brain farts on our part, but there were no injuries... Both were mock attacks... as rats have very sharp teeth it would only take a split second for Cloud to kill Misty. It's going to be another six weeks before Misty is going to be large enough to do intros, and I expect plenty of fireworks, but the fact that Cloud only mock attacked is a promising sign. The first time Amelia got at Max, there was a lot of blood, but they became best friends in the end after Max got her revenge.
So, I don't personally like to give too much advise on the mechanics of intros. So far, we haven't lost any rats yet and we have yet to fail... Some intros were almost instant and very easy and some were bloody and messy. Some very controlled and orderly and others absolutely out of control and one that lasted 3 weeks. I've got a 100% success rate. And I sort of have a process but no recipe. Sometimes intros work due to my clever management and sometimes despite it. But in general they do work out in the end.
Remember, your rats have to fight for status, this is very important to them and will determine how they will interact for the rest of their lives and they know it. One rat may be defending his home and his status while the other doesn't want to be pushed around or in fact wants the top job himself. On the other hand, if you are a real hands on alpha, your guys might not feel there's too much to fight for... you never know how things will play out.
So yes, I'd suggest the oven mitts and persistence, try the carrier method... perhaps or try a really large room with lots of hiding and climbing places, let the rats fight it out, but be ready to step in when necessary... Definitely make sure everyone is bonded to you before trying to intro them to each other.. But in the end the rats are going to do whatever they are going to do and it usually gets worse before it gets better.
I realize that some of the things I've mentioned seem contradictory... It's like teaching someone to cook... If the pan is too cold you will produce a steak as tough as shoe leather, so make sure it's hot.... but if your pan is too hot, you are going to wind up with a blackened steak that's raw on the inside so don't over heat the pan... you need to use the right heat... now how would you explain that to someone who's never cooked a steak before? Thankfully to some degree with rats they will help you out.
I hope that helps.
Best luck.