How can I combine alt-fire and fire(of 2 different weapons) into a single button press?

Solution 1:

What i and a lot of other people do for this kind of thing is use external macro-software and other things similar to that to perform these actions for us.

There is lots of software that can be found on the internet that can do this sort of thing. Like https://www.jitbit.com/macro-recorder/ for instance. The best thing to do is look around and see what works best for you.

Solution 2:

If you have a Corsair keyboard or mouse with buttons, then I would assume you have already thought about this, but just in case, I'll post it anyway.

You can use the Corsair Utility Engine (CUE) to create a macro. I personally have the K95 RGB and use the function/G keys on the left of the keyboard for a variety of macros. In my opinion, this is the quickest solution however, this obviously assumes you have a Corsair keyboard and or mouse.

Coincidentally, Corsair Keyboards are on sale today, August 14th, 2017 on Amazon. They are the deal of the day: Amazon Deal of the Day