I would think a full team of Shadow Mewtwo, Shadow Claw Gengar, or Dark Tyranitar for each member would do the trick. However, I believe we will find out if the tier 5 bosses will be set to Mewtwo’s new HP/CP once we battle the first Deoxys raid. So with Mewtwo’s new HP/CP on Deoxys, I don’t think it can be duo’ed.
Deoxys question
Which Pokemon will be viable for a normal form Deoxys duo? Can it be duo'ed with all movesets or just a specific one? (CB/PB?)
Also if you have a team that can succesfully duo a normal form Deoxys, can you automatically solo an attack form Deoxys?
Answers
Assuming it's a normal tier 5 raid, the following pokemon seem to be viable for duoing: Gengar, Mewtwo, Deoxys-A, Banette, Tyranitar. There are a lot more pokemon that have theoretically enough DPS but will likely lose too much time rejoining.
Soloing the attack forme seems to be possible with Houndoom, Absol, Pinsir, Rayquaza, Scizor, Alakazam, Salamence, Cacturne, Dragonite, Shiftry and SA Moltres in addition to those that can duo normal forme. So it seems the attack forme solo is actually much easier than the normal forme duo.
Data from pokebattler, assuming 30s wasted per rejoin.