Sophos Web Appliance - Content filtering for Wifi connection

Hi there, 

I am trying to find here a solution/suggestion for the situation we are facing:

So, We are using Sophos Web appliance for our Content filtering solution. We lately tried to enable Sophos Web filtering for the WIFI connections in our network. The laptop devices seem to be working fine, but when it comes to mobile devices, it doesn't work. The devices will throw the following errors different devices:

1: "Sophos Web Appliance" isn't configured correctly. Uninstalling "Sophos Web Appliance" usually fixes the problem. Applications that can cause this error include antivirus, firewall, and web-filtering or proxy software.

2: This server could not prove that it is xyz.google.com; its security certificate is not trusted by your device's operating system. This may be caused by a misconfiguration or an attacker intercepting your connection.

3.  Your connection is not private  NET::ERR_CERT_AUTHORITY_INVALID

4. This site can't provide a secure connection  ERR_SSL_PROTOCOL_ERROR

And we did discuss with Sophos Tech support and we were told that the issue is due to the certificates not being installed on the mobile devices.

The problem we see here is that the users who are trying to use the WiFi connection use their personal devices and we will not be able to install the SWA certificate on the user devices.

So I just wanted to post the issue here and see if any of you have an alternate solution.

Thanks in Advance.