* "Ma" and "Pa" are informal terms for "mother" and "father." They are not traditional nouns with clear plural forms.
* You could use the plural forms of "mother" and "father," which would be "mothers" and "fathers."
* You could use "Mamas" and "Papas," which are informal plural forms.
* In a specific context, you might choose a different approach. For example, if you were referring to multiple married couples, you could say "the Mas and Pas."
Ultimately, the best way to express the plural of "ma" and "pa" depends on the specific situation and desired level of formality.