M-Steelix: This set is generally good, it has a lot of offensive presence and can set up Stealth Rock easily thanks to it's great bulk. I think Roar is a better choice than Toxic as it deters setup sweepers, and with Stealth Rocks and Spikes can do a decent amount of damage. You could use Dragon Tail instead of Roar as M-Steelix has an attack of 383 with a positive nature, which could help rack up damage more easily, but Roar can hit through Protect and Substitutes so it's just a matter of preference.
Metagross: This set mostly makes sense, but it's mostly walled by other Steel-types. As one of the primary offensive Pokémon on your team, I'd replace Zen Headbutt with Earthquake for better coverage. If you run Zen Headbutt, there are 47 Pokémon that can resist all of Metagross' moves, while if you run Earthquake only Surskit and Shedinja can resist all three moves. Also, STAB Zen Headbutt has 120 base power and 90% accuracy, while Earthquake has 100 and perfect accuracy, so the difference in power is somewhat negligible considering that you'd want to use Meteor Mash as a primary STAB anyways. However, if you need something to check Fighting-types, then Zen Headbutt isn't a bad option.
Klefki: Klefki can setup spikes, which aids sweeping (see Bronzong) and help M-Steelix with it's phasing. Priority Magnet Rise is a good idea, as opponents may switch into a supposed check (i.e Earthquakers) only to find that their "check" wasn't really a check at all. Toxic is a good move on Klefki for steallbreaking the opponent's walls, as this team somewhat lacks offensive power. As Klefki doesn't have much offensive power, in place of Play Rough you could run Foul Play because it uses the opponent attack stat. If you're worried about opponents with status moves, Klefki can also run Taunt in place of Play Rough.
Bronzong: I'm assuming Bronzong's main niche on your team is setting up dual screens, so perhaps having a setup sweeper could be helpful. The Steel-type doesn't have a ton of those, but one option that comes to mind is Scizor. Scizor can make use of the screens to setup Swords Dances, and can also utilize Trick Room as it's rather slow. Even after the Trick Room ends, it can sweep with Technician-boosted Bullet Punches and make use of the entry hazards on the field. Bronzong has Levitate, obviously helping with Ground-types. Another option for Bronzong is to replace Trick Room with Toxic, because as stated before, this team is rather defensive and this prevents being to reliant on Klefki for stallbreaking.
Durant: While I like the idea of having a fast Steel-type to combat the semi Dark-type weakness on the team, I feel this would be a role better filled by Scizor. Just by running numbers through Pokémon Showdown's damage calculator I can see that against a Gengar (my chosen test subject), a Bullet Punch from Scizor does 90.7% to 107.3%, while Durant's Iron Head does 101.1% to 119.3%. So while Durant does a little more damage with Steel-type moves, Scizor can setup with Swords Dance and deals more damage with it's Bug-type moves (although it's much slower without priority). If you really want to have Durant, you could have a set with Hustle and Hone Claws. After a single boost, Durant's accuracy drop from Hustle is negated while also having a boost in attack from Hustle and Hone Claws.
Probopass: Even with maximum investment and a positive nature, Probopass doesn't really hit hard at all. It has good defensive stats, but a horrible typing which in even more detrimental to your team as it's a Steel-mono. With an air balloon it temporarily negates one of it's weaknesses, but it still has a 4x weakness to Fighting moves. For a special attacker, some good choices are Magnezone or Lucario. They both are useful for checking opposing Steel-types, but Magnezone can also trap them. The problem with it is that it still has a 4x weakness to Ground, meaning that is has to rely on Bronzong for synergy. Lucario has a better speed stat and can boost with Nasty Plot, but has subpar defensive stats. Also, while Lucario is fast for a Steel-type, it's base 90 speed leaves it out paced by a lot of threats.
Overall, your team is a bit defensive in my opinion and could do with a bit of offensive power.