If there are multiple grantors on a mineral deed and one grantee, can the grantee be one of the grantors

The grantee gives the property to the grantor, the grantee can give something to anyone including himself, so yes.

Yes, it is a transfer of ownership. When ownership is transferred all the owners need to grant ownership to another party or parties. One or more of the owners can be one of those parties.

A, B, C, D and E inherited property from their parent. A and E decide to buy out B, C & D. So all 5 need to grant ownership to A & E. Or, in your case, just one party.