Rat Introduction/Dominance

Question
Hi there,
So me and my partner adopted two rats recently from two different sources. One is Oscar - male, 9 months old, the rat rescue person said he is russian cinnamon dumbo rat although we believe he is part wild. He was previously living with two brothers. Second is Ianto - male, a stray rat, part hooded, part wild, about an year old but have never lived in a cage with a companion before as SPCA had no other rat with them and also he might have been abused at some stage as he tends to bite everyone and shows clear signs of being terrified whenever someone puts their hands in the cage. So Ianto lived by himself in a massive cage while Oscar was kept in a not so very good conditions with 2 rats in the same cage and about 20 rats surrounding him in their own cages.
Problem: As we know introducing males could be hard specially both about an year old. So we got a massive two level cage. Oscar lived on top, Ianto lived at the bottom. Oscar was super friendly with me and my partner like instantly although into took about a week to get friendlier with us and not being totally terrified when we pet him or hold him.
Now the introduction...I thought it would be good to just let them meet on neutral grounds but Ianto got too defensive and scratched off a big chunk of Oscar's fur right in the first blow. That instant Oscar got terrified of Ianto and wouldn't even dare come close to anywhere where Ianto was. So we started holding them both in our hands and bringing them close slowly and placing Oscar safely above Ianto's head level so he could gain more confidence. That worked and after about a week when we let them free in the cage they had a decent 20 minute fight but no blood shed, a little squeaks here and there and Oscar came out as dominant one. But Ianto has gone very defensive. He won't let us touch him. He will try his best to not let us bring him out of the cage and he would squeeze in one of the corners of the cage. Its the same behaviour when Oscar is around. Ianto will just freeze as soon as Oscar climbs down to bottom level or even pokes his head from the top when the halfway doors are shut.
Can you please help us as in how to make Ianto more comfortable around Oscar...? They have had their fights here and there but no injuries whatsoever apart from that first meeting. Ianto is so terrified he will only eat if Oscar is out of sight or far away from where he can smell him.
Should we just let them free in the cage and sort it out themselves? Or is there something else we need to do? I should perhaps mention there is no kind of sickness to any of them and they are both healthy and active.
Any help would be much appreciated!
Sam

Answer
There is a process called systematic desensitization, which is basically a process for training an individual to overcome a fear. My book The Complete Guide to Rat Training includes instructions for this. For now, you need to put Ianto in his own cage far removed from Oscar. It is not fair to let him suffer in fear.

See the article called Trust Training on my website for Ianto. You should do this with him until he becomes trusting of you again.  This is basically the same process as systematic desensitization. You gradually train the rat to stay comfortable as you bring the source of fear closer and closer. It must be done very slowly and patiently.

It might also help to have one or both of them neutered.
Deb