Problems with json downloaded from firebase

Hello everyone, and sorry for my English.
I have a problem with Json uncracked from Firebase.
il mi json è questo:


I have tried in every way to write the user ID (the number of letters and digits to be clear), the latitude and longitude to be entered in a map marker. I have to do the same maneuver for all DB registered users.

How can I solve? Which path to pursue?

Thanks Marco