Dual lightning adapter for simultaneous charging/music instrument interface

I presume that you’re attempting to connect an external USB device via Lightning? If so, you’ll want an Apple Lightning to USB3 Camera Adapter:

https://store.apple.com/uk/xc/product/MK0W2ZM/A

This adapter provides both a USB3 Type-A connector and an auxiliary Lightning port with which you can simultaneously connect your iPad Power Adapter.

You will need to confirm the connection requirements of your keyboard.

However, from the perspective of the USB interconnection, then yes - connecting the USB3 Type-A port of the Apple Adapter to a USB Type-B port (be that a mini or micro Type-B connector), the USB bus connection will be correct.

Your Power Adapter is then connected to the auxiliary Lightning port of the Camera Adapter - this providing power to the iPad. It should be noted that the Lightning port of the Adapter can only be used to connect power; this port does not provide a full pass-through of the Lightning connection from the iPad.

With the benefit of more information, it’s now possible to offer further comment...

I presume that you are conversant with USB bus architecture.

The Apple Lightning to USB Adapters, of which there are two variants (I gave you details of the more advanced USB3 version) adds a full USB3 connection with a built-in USB Controller.

If your music device-interface provides a USB controller (i.e, presents a USB Type-A interface), then the adapter will not be suitable for your application. By contrast, if the device presents a Type-B interface, then the Apple Adapter will be suitable - as a USB Root controller is required.