Why do i need to empty my wallet first? Shall I get a different wallet than the coinomi wallet and put them there first? thanks
Because if you don't and you fall from a scam related to the forked coins (BTG and BCH) you will lose not only your forked coins, but your BTC as well. Since they both share the same blockchain until some point, it means that the original private key is also shared. You are not obligated to do it in order to claim your coins, but for your safety DO IT.
I can point you to many cases of people losing all their BTCs because they failed to do this simple step.