If you're pertaining to being able to control your Nest thermostat on multiple devices, you just need to set it up on one of them by following the steps here: https://bit.ly/3r5mJvn
Once done, you have two options which are as follows:
Login to the Nest or Google Home app on the other mobile devices using the same email address and password you used to set up the thermostat.
Add the Gmail account of the other mobile phone's owner as a member of the "house" where your thermostat is. Detailed step by step guide can be found here: https://bit.ly/2K0rOFH
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