Talk Fantasy Football

Do they stack or not?
For egz A buys mercenery Kroxigor and thus now he has 2x Loners, so how does it work on reroll? 4+ 4+? or only 4+?
And where in the CRP rules its written that it stacks or not

You can't stack skills...
page 23 in the rulebook: 7. a skill may only be taken once per player.

so yes hireing a merc bigguy is often "a good idea".

my fellows says that it only takes place for gaining skills on skill roll

Mercenary Loners only need to roll one 4+ to use a reroll.

Skills don't stack, and even if you ignore that and think you have "double" loner the rules don't say you need to roll for each one, just that you need to roll a 4+ to use a team reroll.

ahhh but for every rule there is an ambiguous exception ....
Big Guy AG 1 with double Accurate