The validity of will is governed by the provisions in Wills Ordinance, Cap.30.
Section 4 states the age :
No will made by a person who has not attained full age shall be valid. Full age means 18 years of age.
Section 5 states signing and witnessing of a will :
No will shall be valid unless :-
(a) it is in writing, and signed by the testator, or by some other person in his presence and by his direction;
(b) it appears that the testator intended by his signature to give effect to the will;
(c) the signature is made or acknowledged by the testator in the presence of 2 or more witnesses present at the same time; and
(d) each witness either-
(i) attests and signs the will; or
(ii) acknowledges his signature, in the presence of the testator (but not necessarily in the presence of any other witness), but no form of attestation shall be necessary.
Section 13 states modes of revocation of will :-
(1) No will or part of a will shall be revoked otherwise than-
(a) by marriage ;
(b) by another valid will;
(c) by a written revocation executed in a manner in which the testator could validly execute a will; or
(d) by the burning, tearing or otherwise destroying of it by the testator, or by some person in his presence and by his direction, with the intention of revoking it.
(2) No will shall be revoked by any presumption of an intention on the ground of an alternation in circumstances.
Section 14 states will to be revoked by marriage, except in certain cases.
Sometimes, there will be two or more wills, consistent or inconsistent with each other. It is up to the court to decide on the intention of the testator and make judgment on the validity of each will.