Online Co-op Frame Rate and Lag

Every time I try to play campaign co-op with friends online we have big frame rate problems, with it dropping down very low.
I can play with friend 1 and everything is fine,
if i play with friend 2 we get frame drops and lag,
if friend 1 and friend 2 play together everything is fine,
if the three of us play together it’s laggy.
Friend 2 has the best internet, while me and friend 1 have the same.
is it a connection issue on my end or is there a different problem?

I am having this same issue, anyone else?