choose few options for each filter

-- HikaShop version -- : 2.6.2
-- Joomla version -- : 3.5.1

I wish to improve functionality by adding possibility to choose few options for each filter instead of one, even if one option is already chosen.
What do I have now:
filter "Производители" (Manufacturers) has 5 options (Feather, Parker, Merkur etc). Once I choose 1 options, other options disappear. Photo 1 and 2 show the problem. leza-shaving.com/ru/safety-razors
What do I want:
Once customer chose one option (for example Merkur), he still can choose other options of chosen filter without excluding Merkur (additionally choose Parker and Feather options).
Example: hotline.ua/auto/avtomobilnye-akkumulyatory/16531-5166/

I know that I can partially implement it with "Filter" button, like it`s done here leza-shaving.com/en/straight-razors . thought a customer can`t add options, once he chose some. He is forced to remove filter and set it up again with a new list of options.
It`s obsolete functionality and I wish to remove "Filter" button functionality entirely.

Thx for your help in advance guys