I find some dwarf frogs never get it. The one's your looking to raise are the ones that get it. They will thrive incredible well and be long lived. Patience and persistance are key. It sounds like you have it under control though. Variety is the way to go. Once you introduce spirilina enriched brine shrimp you'll be in good shape as they already like and are used to brine. The enriched brine has a lot more nutrition.
It would not be a bad idea to try some prepared food also. I like just about any formula of NLS (New Life Spectrum). There is no food that can compare to it for fish and amphibians. They have some that are tiny for "baby" animals. I believe Big Al's in Hamilton will have it.