I did mine in Single player, but I helped my friend do it in Multi player. Im no Gold Guru, more of a Silver Slayer ; ) , but we managed without too much of a problem. We selected Geth for the most part, and with the Salarian Engineers Decoy it was pretty straight forward.
Im more than happy to jump in with you at the weekend and try to knock these out, and that goes for anyone else too.
Just let me know when (and what time zone,lol!). mate.