You can pair up all three boys as long as you are aware that you are very likely to have to separate one of the boys at some time during the hormonal teenage months; at least you will have the chance that the remaining two boys will make a stable bond.
Baby nails can be sharp, but they are too short to cut safely.
My Nia's were like razor blades upon her arrival here - you basically just had to look at her to end up with a bloody scratch. It didn't help that she was extremely skittish when I adopted her and her sister. Thankfully, at 10 months old their nails were starting grow not very long after their arrival. When the nails start growing is individually very different; I have cut Tegan's nails at 4 months old (just the very tip), but she was very well developed and well over 800g at that age.