It's fairly likely although not definite. RIRs tend to be a bit bolshy so maybe he will come out as the boss but you will get a bit of warning if they start squaring up to one another, lots of neck stretching and flared out feathers, then jumping around trying to get a peck in before the other one does.
A couple of years ago we had a hatch with a lot of Silkie cockerels in it, they decided to behave like hens and keep a low profile, they had me fooled for a while but as soon as I necked the old cockerel a battle to succeed him started.
I would say it depends entirely on whether one of your boys is happy to be subordinate and how dominant the other is. It's very likely they will fight but not a certainty.