Correct me if im wrong but when you start your server in the properites is say your player count max size like this
"C:\Program Files\mw2 server\iw4m.exe" -dedicated -console +set party_maxplayers 8 +set net_port 28961 +set fs_game "mods/^2gg ^4isnipe" +exec server.cfg +map_rotate
Just change the maxplayers to 16
Then in the mainfloder/server.cfg
Gametype to dm (deathmatch)=FFA
I believe this should fix your problem