Customer purchase order

Dear experts,

my client have many plants some of them behaving as customer for other so i mde inter company stock transfer order in between them.

but after creating it we not get facilities like sales order in production planning ex. for collective conversion of plane orders to production orders (for all materials belong this purchase order ) like sale order.

so we use purchase order which not affecting our vendor plant planning.

so we again make an sales order for this.

may i use purchase order to create sales order if yes then how, or our stock transfer order behaving as sales order for customer plant or it automatically change.

so please suggest how can we make the process so that i only neaded to creat once purchase order or sale order keep in mind customer plant not use MTO it use mts production so purchase order create by it not assigned by any sales order

plz help me

thank you.