Breastrokers and IM» ers require
more lateral leg work to target muscles used in breastroke kicking, which is drastically different in terms of biomechanics from flutter or dolphin kicking.
hands free front squats,
leg press, hyperextensions, crunches of all forms, zercher squats (so long as you don't grab your hands),
leg raises (including side for the glute min / med), some cable awkward cable work could be done so long as you «grip» the cable in the crook of your elbow (front /
lateral raises, pec fly, reverse fly maybe), calf raises, planks, there's
more but they start getting finicky after this lot