It took 3 days to figure out how to do it, without rooting the phone.
But some tools are needed...
I upgraded my phone rom (which came with version 2.26, a modified 1.26), put rom 2.02 then 2.03 and at last 2.05, which is the last one in nubia chinese site.
I used nubia rom updater, for the roms version 2.02 and 2.03 you have to decompress to each folder and point nubia updater to that folder.
The last one (version 2.05), i used option update of the phone.
Then uninstalled every chinese app. Downloaded gapps micro for android 5.0.1 and copy to the internal storage.
Then rebooted the phone with TWRP and installed the zip file. With TWRP root the phone, in advanced menu.
After that, i reboot into android system and made login into google play and updated everything.
It's a google phone now.
I think this should work for Nubia Z7 mini and Nubia Z7 Max
I hope this help someone