DPDT rating combined?
Ratings like that are usually per contact.

However, that doesn't mean you can combine two 20 A contacts in parallel to get a 40 A switch.  You can not count on mechanical contacts to share current equally.  You especially can't count on them to open and close, including all the bounces, at the same time.

Imagine what happens when two switches in parallel open, particularly with a inductive load.  One will inevitably open first.  Since the other is still closed, the voltage will be low, no arc will form, and that switch will open even with a very small air gap.  Now 100 &micro;s later, the other switch starts to open.  At this point all the current is going thru it.  It will arc when the contacts first separate, but will continue to arc much longer than intended due to the high current.

Most of the wear on mechanical switches is when they open.  Closing also causes some stress.  Paralleling multiple switches isn't guaranteed to reduce these stresses on any one switch.

If you want to switch 25 A, use a 25 A switch.  Or, control a relay or transistor with a smaller switch, with the relay or transistor rated for the full current.