Dropshipping questions about split orders, shipping labels, etc

Hello,

I’m looking into adding some dropshipping into our existing store. Right now we sell apparel we print and package ourselves. There are a couple companies that sell items that would be of interest in our market and both are open to doing the drop shipping its just that both would most likely need set up different.

The first one is based in Michigan and their store isn’t Shopify. What would be the best way to send orders and potentially shipping labels to them?

Other partner is local(Iowa) and again their online store isn’t Shopify. I’d need to send orders to them as well but not sure on the shipping.

If someone placed an order where they ordered from one of these items and apparel from our store, how would order fulfillment take place on my end when items would be coming from 2 different locations? Shipping charges?

Any help or direction is appreciated.