How many machamp and mewtwo are required?

I think you are ok on the Machamp department.
Theoretically, people will tell you you need 12 or 18 Mewtwos (6 for every charge move). Since the only use for Focus blast is gyms and Psychic is Machamp raids, you probably only need 6 for Shadow Ball.
The good thing about Mewtwo is that they can be repurposed with charged TMs, so I would say just get 6 if you can, and use them for what you need at the moment.

I have 6 Mewtwo and only use 1.5 of them for specific raids, but I use 6 Machamp multiple times daily...

I think u are good.

Mewtwo isnt really necessary in my opinion. Only use I had out of them (maxed 1, other one ~30) was to solo Hitmonchan and Hitmonlee who are out and probably wont come again.
If you are not sitting on millions of dust I wouldnt invest...

Machamp is very likely to remain the king (or champ, if you will) of fighting-types til Gen 5 when it may likely face competition from Conkeldurr. They will be relevant for the foreseeable future in raids (against Registeel for a couple more days, then Regirock, the ever-present Tyranitar, and eventually Dialga, and as a decent counter to Heatran, etc) and for fighting gyms, as Blissey and Chansey will likely continue to be the most popular/powerful gym defenders. Investing in a team of six is not a bad idea.

As for Mewtwo, it essentially has 3 roles: a bulkier Blissey counter with focus blast, a very strong psychic-type specialist with psychic, and a top-tier generalist and ghost-type specialist with shadow ball. If you have 3 good candidates and enough dust/rare candy, investing in 3 is also a solid idea, though far from necessary, as you could also invest in a single Mewtwo and TM the charge move as needed.

6 Machamps at L35+ is enough. A second team is rarely needed and L30 is enough for that in most cases. Investing stardust to get 6*L40 isn't a bad idea.

Ideal for Mewtwo would be to have 6 with SB, but that's some serious rare candy investment. If you have B/C Tyranitars, Mewtwo really isn't that necessary. I've been doing fine with just 1 Mewtwo and haven't powered up a second one even though I have the candy for it.

Legacy Gengar is obtainable by trading, there are a lot of them just lying around on the accounts of people who never use them. If you have a large community, ask around.

I personally have 1 maxed out 15A Machamp and then I keep a fleet of 5-6 additional weather boosted ones up to L35 (I keep new better ones and trade/trash the others). For my solo attempts and gym wiping I can't find a reason to have more than that, and I just don't like to fight all the time with the same mon. I don't do low-men raids now because of friendship, and I anyway don't have a consistent pal for 4* duos.

Similar thing with Mewtwo: 1x L40, 2x at L30 and the rest waiting for best friendship status to try trading for better IV. I never need more than 3x Mewtwos at any given time, and the L40 just buys me way enough time.

I have 5 Lv40 Machamp and a sixth at Lv36 to reach the attack breakpoint against Tyranitar for duos. I have a second squad of weather-boosted Machamps at lv 34-35 with suboptimal IVs, they are nice to have as backup, but are rarely needed. I recently caught a 100% Machop (my fourth) but I am not sure I will power it up.
I have not yet caught a Mewtwo with good enough IV to power up, but I have not missed it as I have squads of maxed Tyranitars and legacy Gengars at hand.

I think 3 Machamp and 0 Mewtwo are nearly essential for raids and gyms.

Machamps: 6 "maxxed out" with Attack 15 as a minimum, and if you are raiding or clearing gyms enough that you are regularly unable to heal or revive Pokémon, then I'd double that to 12 Machamps and add in 4 Hariyama's. Most of the time Hariyama is nearly as effective as Machamp but it lasts longer in battle, which allows you to conserve Revives. (Also Hariyama is just a cooler Pokémon overall, so nyah.)

Mewtwo: While I understand how useful Mewtwo can be, outside of Mewtwo raids (and the occasional Machamp raid), I haven't found myself powering up a second Mewtwo. I powered up my first good one (IV 80, Atk 13) to level 34, but I don't use it more than once a week - if that. I would LIKE to have a team of 6 "maxxed out" Mewtwo's with good IV's, but unless there are going to be Alakazam or Gengar-esque raid bosses in Gen 4 (ie: Weak to Psychic or Ghost) that I'm going to want to Solo on a regular basis, I'm not likely going to power up any of the 7 Mewtwo I have.

(Yes, I have 7. Yes, I've only powered up 1. I'm not suggesting anyone else do that, only that I have not found Mewtwo to be indispensable or crucial in any way. Other people will have a far different experience than mine.)

4 machamp + 2 hariyama (all C/DP) are fine to duo ttar raids.
Mewtwo, one C/SB is probably all you need. You may also want one with FB to have some diversity/fun clearing blissey.