Is it possible to connect 2 Salesforce platforms to 1 SharePoint system?

Yes it is possible. Please follow the steps below:
Step 1: Authentication request is sent to the adapter by Salesforce.
Step 2: The adapter forwards the request to SharePoint.
Step 3: After authenticating the information, SharePoint passes the security token for further use.
Step 4: The adapter receives the token and thereafter sends it to Salesforce.
Step 5: The token is used as an authentication key, Salesforce then send a request to view the accessible files and folders.
Step 6: The Adapter then forwards the request along with the token and subsequently receives an output. It then again passes on to the Salesforce installation.
Step 7: Either of the two things happen: First being either the token expires and the process is repeated again or secondly using the same token, more requests are sent and received.

Thanks