Probably a NAT issue…
Check your Wifi settings and look for the
NAT-Type.
If its on open its good.
Moderate means you can join but not host.
Strict means you can talk/write to others but thats it, no playing together
Check your Steam settings maybe? These 2 settings. 1st can be lowered if you have problem finding servers. 2nd if your all in each others friends list helps a lot too.