Anyone can help me determine what my turtle species are?

[blazefire99]

I have four large ones and two small ones, I have four red eared sliders (two large two small), a black marsh turtle (I think ) and a turtle that looks like a black marsh turtle but has no patterns (on its face and top shell) but it has a yellow bottom I think, I need to know what turtle species that last one was, oh and any tips on baby turtles? Thanks!