Forgive if any of this is redundant.
As I recall, creating a new profile is fairly straightforward. First you'll need a controller for each boy.
Start console and ensure no profiles are signed in. At the sign in if you scroll right
(pretty sure this is how we did it, been a while ago and I'm not near my console) and there should be an selectable "avatar" to create a new profile, once created this should be
a silver membership and can play locally only. XBL requires a Gold membership so either pony up or redeem code (many games include a code for a month of free XBL) to get the account to Gold level. Repeat for the
next child/account if you need to have a profile for each boy.
For all three of you to play same game at same time, locally or on XBL, said game must support co-op or multi-player play, unfortunately Skyrim does neither. My daughters and I play COD, Halo, etc. (and now Titanfall on the X-one).
and it's a similar sign in process for each game. We usually do co-op mode or a private lobby in multi-player mode is selected and each joins the game using a separate controller and signing into their profile to join the game. I'm pretty sure that is you
only want to play locally, Silver (free) accounts are all that's needed.
I hope this helps, feel free to ask if any of this is unclear.