Id say dual brens is a bit OP. One bren is okay but 2 brens are ridiculous in cover. Make it one slot, give it the dps of the mg42 and itll be easier to balance against axis squads.
The bar would be put in line if its long-range strength was toned down slightly at the same time you don't want to overnerf the Bar as it'll make the upgrade subpar.
And Katitof is right about lmg rifles. Back in the day vet 3 Rifleman's Squads with double 30 cal were insanely strong at all ranges and unkillable with the RA vets. The only real squad that could compete with them were the broken
Obersoldaten at the time.
Bren cant have the same dps as the mg42 because the mg42 is so good to offset grens model count so they can keep dps up. Not only can tommies offset that with a small cost (for all infantry they build) they are also more durable to begin with but also get the same rec acc buff (-23%) a whole vet level sooner
Thr problem with dual wields iis that it allows already superiour units to widen that gap to ungodly unmatchable levels.
Double guns make fresh squads fight like vetted squads and vetted squads near undefeatable.