We have four family members who each have a Facebook account. 

You can sign out of photo gallery with the main MS account at msn.com just find and try to sign in with another family members outlook.com account and when you select publish to Facebook it wants you to sign in and when you do, that email address also is set up with the original msn.com account instead of having a Facebook login that should be setting up and getting information for that Outlook.com email account and not the MSN account.

It seems it is impossible to sign out from the MSN account and sign in with the Outlook.com (another ms account) and have the Facebook icon asking to set up information for the Outlook.com account instead of always picking up with the main account and then associating that main account with the second ms account at Outlook.com.

This does not make any sense at all and I tried removing the msn Facebook account and then tried to add it back in but to no avail as it just keeps using the old account that was set up when Photo gallery was installed on a clean machine. 

Each email sign in through Photo Gallery should have its own Facebook connection.

If I chose to close down my Facebook and another family member was using Photo Gallery then and would never be able to upload to their own Facebook account. This must be a very major bug in Photo Gallery or maybe in windows 8.1 itself?