This question is confusing - talking about double hets or poss hets?

Double hets are easy - pair two recessive visuals together of different mutations and you get true double hets (pied x albino = double het albino pied).

% chance breaks down to parental chances

het x het = 66% het

het x normal = 50% het

66% het x normal = 33% het (poss het)

33% het x normal = don't even bother lol

However, whenever you prove out a gene - your 33% or whatever, het becomes 100% het, and its offspring will then vary based on breeding.