Based on the given conditions:
1. The Manager is the grandfather of U, which means the Manager is male.
2. R, the Salesman, is married to the lady Teacher, implying R is male.
3. The Doctor, S, is married to the Manager, so S must be female.
4. Q is the mother of U and T, implying Q is female.
5. U is the Engineer, and since Q is the mother, U is male.
Thus, the three males in the family are the Manager, R, and U.