Video over that long of a range in France will be quite the challenge with the current EU regulations.
On top of the throughput restrictions discussed here due to the duty cycle compliance, there’s also a 25 mW limit on the ERP which will diminish your effective range.
On that note, after a quick skim of the data sheets on the Heltec modules that you’ve linked don’t appear to be EU spectrum compatible (both list 902-928 MHz). Our MM6108 has RF filters on the module that are spec’d for specific frequency ranges that vary by region, so they’d need to be something like an EU skew for them to perform optimally.
The MM8108 chip has improved upon the MM6108 such that it no longer requires the specific filtering.
We also wouldn’t recommend operating our devices outside of your regional designation because firstly it breaks your local communications body’s regulations, but also likely places you in spectra where the technologies that it’s licensed to will drown out a small IoT board.
The antenna should work fine for the EU, however for your application you’d definitely want to consider running directional antennas instead of omnidirectional to maximize the utilization of your ERP. Assuming your deployment would be line of sight (I hope 
) and rural, you may be able to take advantage of the gains from concentrating your transmission.
For throughput you may be able to burst your throughput based on when you’re taking your shots and have the AP on the camera’s side so that you get more duty cycle.