Is it permissible to massage the feet of family members, relatives, or friends as a service, and is it permissible to practice this as a profession?

It is permissible for you to massage the feet of your maternal cousin's son and other men, as long as there is no deviance in it; otherwise, it is forbidden, because what is permissible becomes forbidden if it is intended for lust. As for your colleague's work in massage, it is not permissible if the massage is for women, or for men if it results in looking at or touching their private parts (awrat).