Can I install 2 30 amp twist lock receptacles in a 2 gang box on 1 circuit?
This keeps coming up: The question of whether you can put more than one receptacle on a 30A circuit.  

All the receptacles must be 30A.   (NEC 210.2B3) 

It's very surprising to find 30A plugs on machines that fall considerably short of 30A. Generally they use a 15A or 20A plug if they are able.  

I'm not sure you can fit two of those connectors two abreast in a 2-gang box.  That's a mighty tight fit, and I'm concerned with the screws striking each other.

It'll be tight and awkward to grab, and depending on the plug, they might interfere. I'd go a double-gang bolted to a single-gang with a conduit nipple. 

Big receptacles don't have 2 screws, so you'll need to pigtail them.  The extra wire count will mean you'll have a lot of box fill, in both the Code requirements and in the actual sense. You'll need a very deep box.