Webmail sign-in works on one computer but not the other...

Hello! I am attempting to sign in to the same email across two different devices, both laptops, and while it is working on mine to see all the new emails the other device is claiming that the Xfinity ID or password is incorrect even though I am inputting it exactly the same as the first laptop. My spouse and I share an email and we want to be able to respond to relevant messages for each of us at the same time which is why we are attempting to open it on separate laptops. 
I would ideally like it to be in Outlook, but since outlook is not syncing with our Xfinity account (something many people on the Microsoft forums have also been noticing for the past few months) the next best step is for us to be able to open it up in webmail simultaneously. I am connecting with support from microsoft to see why outlook isnt working since I do not believe Xfinity is to blame if I am able to access it on one laptop (not that microsoft has responded). I just want my spouse to be able to get on webmail at the same time as me. What can be done to fix this? 

Thank you in advance for any help or advice!