Answer:
(Fatwa: 990/933=B/1430)
The son-in-law of your khala (sister of your mother) is not a mahram for your mother, it is unlawful to go for hajj with him, she will be sinful. However, if she goes and performs hajj, the hajj will be valid but makrooh.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband
