I am using Skype (Beta) 18.104.22.168 on my Ubuntu and after some trial I believe that it is not possible to block a whole bunch or group of contacts all in one move.
It would be a very handy feature: being able to block entire groups might avoid the need to create two different Skype accounts, which is the current trend seemingly.
In this link here it seems that by selecting 2+ contacts one is able to block them all in a row. I guess this is valid for the Windows version however.
Can you confirm all of this?