Hello NiallJordan2
Thank you for participating in the Microsoft Community, I am Skypper G. I am an independent advisor, let me help you with this
There is not option to do that, however both account can share their content and use OneDrive as storage to keep their files shared.
Then, depending on their Office 365 subscription they can keep just one and share the subscription, see:
https://support.microsoft.com/en-us/office/shar...