Stuck in lobby when trying to joins friends,PC to PC,nothing loading

HI,my son is trying to play and joins his friends that both have pc like him,when he tried joining,nothing boots or load and he appears in the lobby but nothing is loading for the next step,

i tried disabling firewall,anitvirus,etc

GS3 is up to date so is windows

ive seen a few peoples complaining about this issue without any fixes,any ideas of whats going on and how to solve the issue

both his friends have a pc like him and he tried to join them (trying each time when they are alone to play the 2 together)

thanks in advance