Hi Ashley,
Legally, after the death of grandparents the property automatically came to be vested in your father and his siblings equally, and in case of they having expired before then in their progeny/children. The fact that they are not interested in property won't make you the owner directly. You have to have a registered relinquishment deed from them in order to transfer the property in your exclusive name.
And as regards the second part of your query - you can adopt your brother in law if there is 21 years age difference both as regards you and your spouse.