The A7 has better specs in all areas when compared to the other two except for one feature- Google Play Services- which only the A5 has. That too only the A5 from Cect – as far as I know. You can try browsing on Aliexpress, maybe there are sellers there who provide it with GPlay too.
Otherwise, the A7 is an upgrade in all other areas whether you’re talking about the camera, the screen resolution, the battery or the screen size.
But the size might be too big for some with the preference being for the smaller A5 and A5 pro. 6.7inches is definitely huge (that’s not what she said) especially for one that’s not without bezels (unlike popular mainstream smartphones which have no or very little bezels). Having said that, since many people will be using this as an e-reader too, the bigger size will make for a better reading experience. The same goes for those with bad eyesight.
In conclusion, each device has its own pros and cons and depending on your needs, one will be preferred over the other. Hope the above table helps you make your buying decision.