Which muscles of the pelvic floor should be strengthened to help control urinary control?

All. The pelvic floor exercises called "kegel exercises" are the exercises prescribed for the whole pelvic floor. They must be done faithfully and for many weeks to be effective. I have prescribed them many times but most of my patients were not motivated to continue for the length of time needed despite many reminders.
Public-coccygeal. The pelvic floor is a hammock and it consists of three parts. The part which extends from pubic bone to coccyx is particularly important for urinary control, kegel exercises are designed to strengthen this muscle.