I have not had much time to continue this project since last month. Maybe this state will change next month and I will make some progress but now only thing I managed to do was replace the modems for my copters.
I did sold e3276 modem and currently and I use only Huawei e3372h modem for both copters which seem to be the best solution for both Raspberry pi3 and Raspberry pi0w.It works perfect.This model as provided by the manufacturer has support for IPv6 protocol therefore it was my final choice.
I hope that last month I will manage to order some additional elements for both models and project will relaunch again.