You can go to Homepath.com to see current status of Fannie Mae Michigan listings.
This can be a very frustrating journey now a days...good luck, and hang in there!
If the sellers have signed the purchase agreement, then you have an accepted offer and the sellers can not look at any other offers other than back up offers.
Until both parties have agreed and signed the PA the home is open to any offers. Normally if Fannie Mae has verbally agreed they honor there agreement until they process it and send you a signed PA back. You should not be going to another highest and best situation. I would question the listing agent.
If yes, that is a problem. But if the purchase agreement was never fully in writing, then the seller can still look at more offers.