A: The father-in-law is a mahram for the daughter-in-law since he is perpetually haraam for her to marry. However, since this is a time of fitnah, all precautionary measures should be taken when they have to travel together especially if both are young e.g. Both of them should avoid being in seclusion, they maintain a distance between themselves etc.
And Allah Ta'ala Knows Best
Shafiq Jakhura (Mufti) M.D. Mangera (Mufti)
Fatwa Dept. Fatwa Dept.