Tier points and other using the 2-4-1 voucher

Wasn't able to find anything related to this specifically so here it goes:

-if I use the 2-4-1 voucher that I got with the BA+ cc on a paid ticket do both passengers get tier points?
-is it possible to use the 2-4-1- voucher on a redemption ticket?
-is it possible to buy a Y ticket, upgrade withe miles to C and use the 2-4-1 voucher:
-would the 2nd traveller be in the same class?

Would love to hear form someone that has used the voucher.

Cheers