Publish Unity 3D iOS app as testers app on Apple Test flight for internal use for my client

Hi, I have a ios VR app build done in Unity 3D, ready to publish for my client. We are not going into the store. The app is only going to be for internal use. Client has 12 email addresses of internal staff that need the app and possibly another 5 would need the app as well. I need someone with an Apple developer account. That will tkae my app. Publish on XCODE, check it works and functions on iPhone devices as I don't have an iPhone to test it. Then setup the app for testglight. Send invites to clients 12 emails. Re-publish the app every 3 months so that client can be allowed access. i need to provide 1 year support to client. So, means we need to send an update build for them to have the app on there devices 4 times, every 3 months if the app expires in 3 months, Please advise. So basically looking for someone reliable to setup the app for testing, send invites out and do this say 3 or 4 times so the client has a working app when needed. Thanks.