Hey guys i need help

i bought another copy of Ravenshield cause we got 2 pc`s here and wanted too play together

now i got 2 different cdkeys put in on the pc and laptop

and whenever 1pc aint in a game the other can join a server

but as soon as 1 pc is in de server and i wanna bring my second pc it says cdkey in use while we got 2 different numbers

i know it is cause were on same router and lanned but i dont know why it wont just join the server we got both different cdkey yet it says cdkey in use please help we wanna play together on Ravenshield...