I think it's not necessary a problem if two or more pcn overlap. I don't believe you could avoid it. But just one of them may count for fulfilling the rule.
I think pcn/npcn are the right categories for the non-touching rule, but for the placement rule I suggest something else.
Maybe
"Mark 16 diagonally connected pairs of squares (plus 4 single squares?) that do not overlap. Then solve the Sudoku so that the marked pairs (plus ...?) contain each 2-digit (less than 100?) prime number."
Of course just if this is what you mean.
And another thought: If the rules are not ambiguous, it doesn't suit to the fun fact you want to describe. But the Sudoku rules (plus maybe some givens) will solve this problem.
I think pcn/npcn are the right categories for the non-touching rule, but for the placement rule I suggest something else.
Maybe
"Mark 16 diagonally connected pairs of squares (plus 4 single squares?) that do not overlap. Then solve the Sudoku so that the marked pairs (plus ...?) contain each 2-digit (less than 100?) prime number."
Of course just if this is what you mean.
And another thought: If the rules are not ambiguous, it doesn't suit to the fun fact you want to describe. But the Sudoku rules (plus maybe some givens) will solve this problem.