As far as using two phones to control the Shark ION 750, I would just download the app to both phones and test that. I don't see any reason that you would have a problem connecting to it from both phones. Essentially you are linking to a wireless device through your network so you should be able to do that with multiple devices. For example, you can also control it with Alexa and Google Home.
As far as getting a remote, I don't think it possible. The vacuum connects to your network. Most remotes use infrared beams to send information to devices and I don't think the Shark ION 750 is capable of receiving control messages via infrared.