Kaddish for father in law

My husband is saying kaddish for my father who died on 7th of Nissan 5770. my question is because my husband is not a direct decendent even though he was extremely close to my father, does he say kaddish 11 months or 12 months. thank you ,

Since the punishment of the wicked in Gehinom is for 12 months, and one does not want to assume that one's parents were wicked therefore out of respect for one's parents the minhag is to say only for 11 months. However this reason does not apply for someone who is not a son. Therefore, according to Rav Tokachinsky on Gesher Hachaim(Vol. I, chap. 30, 9,4 ) that it is proper to say Kaddish 12 months. Nonetheless, he mentions that the custom held by many is to say for 11 months. Besorot Tovot