I think even the sister Miyuki is stronger than Mayumi and Mari, if you look only into their amount of mp. But Miyuki never fight them so it's difficult to say who's stronger in real battle.
Spoiler for magic:
And their magics are different to each other, no people have the same magic(because its more to family's, each family have their own magic), though But ofc they can use the low level/common magic too, not only their family's.
For example, Jumonji's magic(and his family's) is one that create folds of varied magic shields around the user and repel most kind of magics. Its like he turned into a magic tank if he runs into horde of enemies and crushed them all.
For other example, Mayumi's good at precise aiming and her magic is one air bullet that pierces through its target(maybe wrong cause I don't remember the detail that well
)
So which one is stronger or weaker, the answer is relative based on what opponent/magic they're fighting.
And no they(MC & the big 3) haven't fight even once.