Just to keep things simple to start, this line should be all you need:
You can add any additional parameters once you get the basic setup running.
Did you check Device Manager to see if all 3 GPUs are showing up? It should look like the image below, but with 3 just gpu's showing:
What is the amount of hash rate you are getting with 4 x R7 ?Code:
ethminer.exe --farm-recheck 200 -F -G http://eth-eu.dwarfpool.com:80/address/Worker1
You can add any additional parameters once you get the basic setup running.
Did you check Device Manager to see if all 3 GPUs are showing up? It should look like the image below, but with 3 just gpu's showing: