I think prioritizing the wide lens is the right choice. Glacier is not like Yellowstone in terms of wildlife - you'll be lucky to see a large animal and chances are that it will be off in the distance although for that rare occasion it would be nice to have something available. (Marmots and chipmunks are plentiful though
Obviously either the 12-24 or a wide prime would compliment your 24-60 nicely. I personally like to have macro capability along on trips like that - your Sigma 70-300 is probably macro but a relatively cheap way to get a lot more IQ is an old 50 to 135mm prime on a set of cheap manual extension tubes - viva la green button! Glacier is one of my favorite places, your really going to enjoy it. (Keep in mind July can still be quite cool and sometimes damp - hopefully not, but be prepared).