Required Microsoft Office 365 freelancer for Microsoft Word Office 365 subscription sharing job

I need help with Microsoft word office 365 sharing. I have the subscription which I can put office 365 on six computers. Here is my problem: I put Microsoft office 365 subscription on my computer and on my sons computer. They are both under the same user ID.
I saved "Document A"under OnrDrive on my computer which also shows on my sons computer since we are both under the same subscription. PRoblem: I want my son who is also under the same subscription to be able to edit the document with me but I want to be able to SEE his changes AND I want to know the items that HE changed.
Right now when he changes something and I change something it shows the "same person" changing it since were under the same subscription. How can I fix this?

AND I don't want to use Google Docs. I want to use Word only!

Skills & Expertise Required

Microsoft Office 365