Your itinerary is:
- Nairobi, Kenya.
- Paris, France.
- SXM = Princess Juliana airport in Sint Maarten, a Dutch overseas territory.
Only the second step is in the Schengen Area. So the allegation that “the passengers transit in two Schengen countries” is definitely wrong. That would be the case for a double transfer in Paris and Amsterdam, for example. But not for a single transfer in Europe. The Schengen area only consists of territories in Europe and close to Europe, including islands in the North Atlantic and Spanish territories on the coast of North Africa, but not including any place in the Caribbean.
The Paris CDG (Roissy) airport allows airside transit if you are connecting between two non-Schengen flights on a single ticket. Most nationalities (including Kenyan) do not need a visa for airside transit. The rules for needing an airside transit spell out when you need one: in terms of flight destinations, it is solely based on the Schengen Area. You do need to be careful about general statements which could plausibly have an exception for overseas territories of an EU countries, but this French government page does cover overseas territories and mentions no such exception. So flights to Sint Maarten do count as flights to a non-Schengen territory, so they depart from and arrive at the “international” (more properly: non-Schengen) zone of the airport. For a connection NBO-CDG-SXM, you do not need to enter France.
By the way, even flights to/from French overseas territories depart from and arrive at the non-Schengen zone of the airport. This is a minor point of political contention since these are domestic flights.
At SXM, I can't find an official source, but I see multiple sites that state that nobody needs a transit visa providing that you have a connection on a single ticket and are transiting on the same day (the airport closes at night, so for a next-day connection, some nationalities need a tourist visa for Sint Maarten).