melholly, it sounds like both the mums are 2007-born or older, so only needed one tag. (Have I got the year right? I think double-tagging came in for 2008-born lambs, didn't it? Then EID for 2010-born.) Assume that they predate double-tagging anyway - check with the farmer you got them from and/or get someone who knows how to check how many 'big teeth' they've got and how old that makes them.
If you've got new tags they'll come with instructions - if you do it as shown and with conviction, it won't hurt - honest.
Your paired tags should have one yellow (the chip is in this one) and one other colour - this has no chip in it.