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those red hermits look like mexican red legs that I have seen before. But they could also be much larger species. I looked around for those hairy looking ones and all I could come p with is that they are probably predatory. The little red guy almost looks like a mithrax crab but the claws aren't quite right.
The first three crab pics I would agree are probably preditory. Although, not much of a threat while small, they may be later on. The red crab in the middle does look like a mythrax crab. An algae eater like the emerald.
The last hermit looks like a scarlet hermite, a great addition. The red looking one looks like a mythrax like fluff said.
The hairy looking crabs could be a type of decorator crab but I doubt it. In a tank your size, they shouldn't be too much of a problem, as long as they stay somewhat small you might be in the clear. You could try setting up some glass cup traps baited with some meaty foods.