registration required or not

In case of a purchase of single rented property in the name of 2 individual for example Mr A and Mr B.
where Mr A is registered under GST Act and Mr B is unregistered.
The rent invoices made separately by both of them.
The question is about the charging of GST on rent invoice??
Is Mr A only to charge GST in his bill or both have to charge and get registered under GST??
Please suggest the right solution..