Thanks to Bev (Texas Belle) for suggesting Rescue Remedy!  I am happy to report that it seems to be making a real difference in Osiris. 

We have been giving it to him about an hour before sunset (when he has been acting strange) and he is now much more calm, not acting scared and staying upstairs with us!!  Also, I was cooking and he was right there in the kitchen with me like he always used to be.

Also, PixieBee, I have been using your suggestions for redirection of his attention.  You all have been so helpful!

I have also made an effort to have some one on one time with him lately.  Dave takes the baby for a bit and I play with Osiris and give him lots of attention.  I think that is helping, too.

And I don't know if it was just a fluke or not, but tonight, people were shooting off fireworks and he wasn't shaking like he usually does!!

We are also using the Good Behavior Pheremone Collar.  I think that is helping too.

Thanks to everyone's good advice - hopefully we can keep having good nights!