Hi Bob,
according to your Info we can exclude overfeeding;
10 micro crickets in two weeks for 2 juvenile Fire Salamanders seems too little to me, and in addition to that, you should alter different food types (of which Ester already mentioned an other example).
In my opinion, the best food is self-caught insects, earthworms etc. from the wild (if it´s possible for you to do so).
Is the kitchen roll always that wet, as it looks in the picture? Do the Sals have the possibility to chose hiding places with different humidity?