I finally got it working! The problem wasn't the actual transmission, but instead the auto-acknowledgement. The remote uses the auto-ack feature of the nRF24 to know if the transmission was a succes or not, however I had not taken into consideration that a transmission could be succesfull even though the auto-ack wasn't recieved probably.
And it seems that the nRF24 modules weren't to blame, but instead the poor quality of my Arduino Nanos 3.3V output. Apparently the clones that are being sold on Ebay etc. comes with a very poor 3.3V regulator, that causes a lot of electronic noise - some worse than others. The noise/voltage ripples can make signal distorted and therefore not getting to the remote.
I solved this by adding a 220uF cap on the 3.3V rail, and adding a 47uF on the nRF24 modules (soldered it directly to the pins). This however didn't solve the issue completly, I had to make some software changes on the receiver, and now the remote works perfectly with a distance of +8 meters.
I will update the software on githup tonight and finish the schematics as soon as I can
@JdogAwesome Thanks ! I have choosen to use nRF24 module, because they are power efficient, and easy to get and use. The idea of the remote, was that anyone with a little DIY-skills should be able to make one by themself, and therefore I believe that an Arduino and the nRF24 modules are a perfect match