Dhana settlement(deed)

Your in-laws, during their lifetime,  can dispose of their property at their discretion. Your wife is a legal heir to the property,  if any, left intestate their lifetime irrespective of the property, if any, conveyed to her earlier.

If you are paying consideration for the property you have to go for a sale deed which is the best.  Otherwise, if the property as their own, they can gift some property to your wife without consideration(price amount).

Thanks Venu Sir

If your mother in law is desirous of transferring her property to her daughter by executing a registered Dhana settlement deed, then your wife will become an absolute owner of the property 

With regards to other property, if your mother in law  is dying intestate, then your wife as one of her legal heirs, shall be entitled to share in the other properties too. 

Thanks Kavksatarayana and Kalaiselvan Sir