How to make apps know that I actually have internet /make them not check for wifi etc when I'm reverse tethering? I've researched the issue of some apps not connecting properly to internet  and it is caused by the apps checking the state of wifi and other standard Android internet connections instead of actually trying to connect to internet which makes them not connect to internet even though the device is connected. 

I've also done what the thread at XDADev says with the reverse tether guide:
netcfg rmnet0 dhcp and other netcfg (like wlan0 and p2p0 which appear after you turn on wifi. (They appear as a response to ifconfig.))

How do I fool them?/Make them know I am connected?
The best answer is that you can't. Apps act on their programming and unless you plan to modify significant parts of Android, what you want is not easily done (if at all).