Where is this internal manufacturing? is it a second plant or is it in the same plant?
As you wrote in-house, I assume it is just in the same plant, and then I cannot imagine for what reason one needs a PR, a PO, and especially a sales order for this process.
PR and PO are used for external procurement and stock transfers. Sales orders usually as well for external sales.
An internal manufacturing would usually be done with work order or production order.