With prep, I can see them pulling it off with difficulty. It's different than fighting Thanos, but Magneto cannot take a serious hit from anyone like Thanos. Beast got behind an older and more experienced Magneto, so I don't see why Strange can't create a portal and have Spider-Man quickly jump through and one-shot when the opportunity presents itself. They didn't reveal everyone to Thanos, so they won't here. Even Magneto's force fields can't stop portals from working. Remember that Dr Strange will also know Magneto's power through seeing multiple futures.
Magneto can sense metal, if he's out for the kill like in X-men Apocalypse (when his daughter dies) then I'd say he wins as most people have some sort of metal on them which he can sense from great distances away. Plus with his shield which am not sure if they can break through it. He'd kill most of them extremely quickly.