I think if you're in ski school you'll be fine. They have a lot of experience of getting people skilled enough to ski enough trails by the end of the week that people enjoy themselves (it's in their interest !). The ski school guarantees that after 2 full days you'll be doing Whitefeather (the easiest frontside green) but Bonanza & Jesses (accessed via lift 8) are not any more difficult in my opinion. As soon as they're comfortable there, let them try 'round the world' which is a long run (around 3 miles ??) consisting of lift 1 to whitefeather to lift 2, up lift 2 to Honeysuckle, then all the way down the back to Winkelreid, then Rubezahl all the way back to Lift 1. Stamina is more of a problem ! (It will probably take over 30 minutes the first time anyone does it !) Easiest blues I think are Bambi on the front & Maxies & Shalako on the back. Most demanding blues are probably Porcupine on the front & Lonestar on the back.
I've never skied Breck, but I skied Copper & A basin last season and I thought there was MAYBE half a grade difference between Taos & Copper (i.e. an easy blue at Copper was like a more difficult green at Taos) - just my opinion.
Take advice from the ski instructors & I bet you'll have a blast.
There are a couple of other taos threads here - try this one
and if you have more specific questions pm me or post again here
Oh and if you are staying in Taos try the mexican food at Orlando's in El Prado which is between Taos and the Ski valley - it regularly gets the best mexican food in taos award.