Bill to - Ship to under GST

Hello
one of my client sells heavy art pieces and decoratives Sometimes Bill to and ship to are in different state, how the GST will be charged in following:
1. Mr.A in Maharashtra buys goods from Mr.B in Maharashtra and tells him to Deliver at his other branch in Gujarat and bill will be paid by Mr.A, whether Mr.B should charge IGST or SGST/CGST? and how the ewaybill will be generated as invoice would be having name of Mr.A?


2. Mr.A in Gujarat buys goods from Mr.B in Maharashtra and tells him to Deliver at his other branch in Maharashtra and bill will be paid by Mr.A, whether Mr.B should charge IGST or SGST/CGST? and how the ewaybill will be generated as invoice would be having name of Mr.A?
Thank you