Is it possible to use the same eWeLink account on multiple devices?

Unfortunately, eWeLink app does not support using the same account on multiple devices simultaneously.

For example, if you have logged in your account on one phone and try to use the same account on another, then the login info on the previous one will expire and you will be logged out automatically on the last phone. 

The only exception is eWeLink Web, which works on PC/Mac. Since the platform of the web version does not conflict with mobile device, you can use the same account on your phone and on PC/Mac at the same time.