Status of a waqf made by a kafir

Q: I request clarification on the ruling of waqf made by a kaafir.

What is the status of a waqf made by a kaafir? For example, if a kafir makes waqf of land for the building of a masjid, is such a waqf valid in Shari‘ah? [Kindly clarify, and also refer to Imdadul Ahkam, where there is mention of a related fatwa regarding this mas'ala]. 

Giving zakaat to one's brother in law

Q: Is my brother in law a recipient of zakaat? 

My sister and her husband have a few debts but at the same time they have a TV and phones and Alhamdulillah food in their home, water and electricity, and a nice home to live in even though it is on rent. 

We feel it will be incorrect to give zakaat to them because they are not termed under masakeen, poor or destitute but they do have debts to finish off.

My brother in law has recently opened his own business and slowly getting onto his feet.