Hello,
I have a question: this MS-SQL Server on Microsoft Cloud or Desktop PC?
If on desktop PC, then we dont need PHP or ColdFusion but a simple and light apps agent. Otherwise, we would use PHP. I should also confirm you that both calendar system require an oauth2 authentication, it means it requires manual user authorization on each account you need to sync. This part would be coded by me also.
So, let me know your comment
Regarrds,
Ningsih