Minimum group size for tier 4 raids?

T-Tar needs 4/5 high level players to be safe. Same with Lax, Blastoise, Venusaur, Charizard and Rhydon (possibly 3/4). Lapras needs 5 to be safe but we've done it with 4.

This assumes no one is tossing in Blissey's and Lax's on attack.

I almost got Tyranitar with a group of 3 yesterday, over 90% defeated. I'm level 34 along with two 27s, one being my wife who isn't really into the battling details. I'm favoriting and powering up the correct teams for her and me. However, I think the bosses' moves matter a bunch, too, the one we fought was using fire blast--which is obviously easier, so it'll vary whether 3, 4, or 5 is necessary to win

Successfully did Snorlax with 4. Levels 38, 35, 33, 27. Heard tyranitar needs 5.

Rhydon can be done with 3. I think the others can be done with 4 with higher level players and proper counters.

As long as the players are of reasonable level and using the correct types, you should be fine with 4/5 players.

With random unknowns however, I'd probably double that to be on the safe side. There's a lot of novice players out there who make poor decisions in pokemon selection - as an example, I did a Blastoise raid today and one player said he was going to use his Rhydon (admittedly he was a younger player and I did point out his error).

We beat a Lapras with 4, but it helped that it had Hydro Pump. I'm not confident we could have taken an Ice Beam Lapras with 4.

I did Tyranitar with 4 and I bugged out - invisible bug - so frustrating. Levels 30, 36, 38 and 39. Beat him with 3 seconds left but if I didn't bug out it would have been a "bit" quicker.

2 people (Lvl 40s) in Japan did a Tyranitar where 1 guy had 4 maxed Machamps and 2 filler Machamps (level 20 and one much lower I think...) Had like 10 secs to spare...

Here is the video:
https://www.youtube.com/watch?v=VpMStuoKPdM

The video also showed he didn't lag much at battle start (I lag 27 secs normally at start)...

The Tyranitar had Stone Edge.

Ultimately, it will really depend on the mons that the group has...and if powered up...

Mons without the double weakness (like Tyranitar) would probably need more than 2 though...

I saw a Tyranitar taken down with a group of 4, one of whom was level 23. It's definitely doable, just depends on levels and Pokemon used.

5 is safe
did it yesterday with 4 33-35 and one poorly equipped 28 with 17 seconds left (most mons only powered to 30)
would advise if there is a weak supporting player in the group that they should have a tank as their last mon and aim to dodge all when on last mon. Her last mon died just as we beat it and she missed bonus round.

Personally, I would have tried it with the three of you. If you end up failing and losing your raid pass, it is just one of 30 free raid passes you will get in the next month (and you will presumably also get 1500 coins).