Android engineers, to want ios, you need ios engineers, java or C or C++ engineers. This is the most basic, provided that your engineer or yourself has the ability of product manager and ui designer. If you don't have this ability, then you need a product manager to take charge of the overall product concept, and you need UI designers and interaction designers. With the above, you can develop an APP.
But what about after the development is completed? Still have to put it into market operation, right? Therefore, you also need promotion and operation personnel.