I completely understand your frustration with swimmy feet. Unfortunately, because the skeletal hierarchy is basically pure FK by default, it happens fairly often (just imagine how hard it would be to lock a character’s feet down in Maya or Max if the legs were FK). There is, however, a really easy solution: use UE4’s two-bone IK. Documentation here: LINK.
FYI, at Epic, we include extra bones for IK in the skeletal hierarchy, which are children of the root and are constrained to the foot (and hand) bones in Maya. We then use those bones as the End Effectors in the two bone IK setup in UE4. Take a look at the skeletal mesh in the Third Person Template to see an example hierarchy w/ IK bones and there are several examples of IK setups on AnswerHub, in the animation demolet, etc.
Just yell if you have any other questions.