M is father of D. M has only two children. D is the brother of C. C is the daughter of K. T is the granddaughter of K. U is the father of T. How is U related to D?

M has two children, D and C.

D is the brother of C, hence D is male. C is daughter of K, hence C is female and K is the wife of M.

T is the granddaughter of K, meaning T is either D or C's daughter. U is the father of T, meaning U is the husband of C.

Since D is the brother of C, U and D are brother-in-laws.