are apps 'multi licence'?

As long as you use the same Apple ID, you can redownload them on multiple Macs for free.

 

They certainly can. Not sure why the prior reply assumed that all your apps were from the Mac App Store.

 

As a poster above noted, it depends on the software. Devonthink and Scrivener , I think, allow multiple installations along the lines of the note below:

From the Devonthink forum:
"It's possible to install the software on multiple computers as long as you're using it only on one at the same time."

I think Scrivener is similar, but their website is currently down, so I can't verify. Except that to use on both Mac and PC, you must have two licenses, one for Mac and one for Windows (which I do).

Wolfram's Mathematica is an example of software that is not allowed on multiple machines. Indeed they are paranoid in their licensing approach.

Microsoft is similar: Office for Mac: One Copy per Device. You may install one copy of the software on one device. That device is the “licensed
device.”