Brother in law

Right I'm British, mrs has finally got her Indefinite-leave-to-remain and we will be applying for her citizenship soon, i want to bring her brother over for a visit, what im not sure off is it a visit visa that we apply and who applies me or the mrs or doesn't it matter who applies?

Also shall we wait and get her british citizenship first ?

Your brother needs to apply for a visitor visa: https://www.gov.uk/standard-visitor
Your and wife's future British citizenship has not bearing on your brother's application.

Nice one thanks