Okay, I had a look at your pics. You have some really nice shots of them and they are all very nicely chubby! Congrats! Alto and Hilo definately qualify for Buddha Belly awards and Niko and Pako are not far behind. So, here is my verdict:

Niko-girl.
Hilo-girl.
Pako-girl.
Alto-not 100%, but I am leaning towards boy.

Alto has a darker throat then the others for sure. It does not look the same as Yoki's, but if you have heard calling, I would place my bet on Alto being the culprit. Great looking frogs-job well done, Lesley.