Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi Jian,
Office 365 Home subscription can be shared with up to four other people. If you already have 5 devices added on your Office subscription licenses and you want to add a new Office Home subscription using the same Microsoft account you've used to purchased your recent subscription, the Office subscription will only get stack. Meaning, it will only add the months or years you subscribe to Office.
Purchasing of additional subscription to add another 5 device license is yet to be determined. Our developers are collating suggestions for the improvement of your experience in using Office 365 Home. Since this feature is not yet available, we encourage that you submit this as a request through the Office 365 UserVoice.
Thank you for your kind understanding. Feel free to post back should you need further assistance.