From (1) and (3), T can not be the only daughter and have a sister (R or S). Hence, T is T’s brother i.e. D is a Male.

From (3), let’s say that R is T’s sister i.e. R is Female.

From (2), Q is S’s only son i.e. Q is Male.

But T is Q’s brother which means that Q is not S’s only son. Hence, our assumption was wrong. Thus, S is T’s sister i.e. S is Female. And R must be S’s only son. Now it is clear that T & R are Males and S is Female. Q must be a Male as only one of them is of opposite sex from each of the other three. And he is S & T’s brother.