Best thing to do is research both species online, find out what their natural foods are, make sure your tank is setup correctly with correct water and air temps, land areas, etc. Also, frequency adults need to eat. Some may not need to be fed more than a few times a week, others may need daily feedings. I just don't know enough about these newts to say what could be mission or what is normal.
Google.com is a great search engine to find articles, caresheets etc about various reptiles and amphibians. Read as many as you can find, some will of course have conflicting information but often from the differences, you can find the correct balance that works for you. Checking your local library,bookstore,herp society can also reveal books and information about caring for these two kinds of newts.
Another note, if they are used to eating pellets, that may be why they are refusing to try new items. Try feeding them the same kind of pellets they were fed before, then once they are eating normally, you can mix in different food sources for variety.
Also, if they are very recent additions to your collection, they may still be in the process of getting used to their new home. Most reptiles take a week or two to get used to their new home.