The emotional item called attachment within the family members is the height of stupidity being done by even highly educated people. If they are so much sentimentally attached or emotionally woven, they should forget what they have done, giving the labels like trust, belief, faith will not work out in this material world. Everyone are behind the material or money whether rich or poor, so there is no surprise that his own elder brother indulged in cheating spree by breaching the trust and faith reposed by his brother on him, leaving him to toil in lurch due to his greedy intention/ambition.
The solution legally is not visible now however, your brother in law may write to his brother giving the details of the periodical money transfer, ATM withdrawals by his elder brother and ask him to give his share in the property that is existing and also a share in the sale consideration amount from the property disposed. Make his brother to commit by giving a reply either accepting or denying the same after which a cleverly planned legal demand notice can be sent to him subsequent to which a suit can be filed for relief.
Consult an expert lawyer who will suggest you more ideas based on the circumstances heard in person.