Hey cman, welcome to the board......
Not sure where the best place to get tickets would be.
I know you can sometimes find good deals on EBAY.
As far as staying away from certain areas, I really don't think you have anything to worry about.
Texan fans as a group are usually pretty mild with opposing teams fans.
Of course, as with any group, there are sometimes exceptions.....
The rowdiest section at Reliant Stadium is known as "The Bull Pen"
It's the seats in the north endzone, sections 116 & 117.
I doubt there would be any seats available there, but you and your family would probably enjoy a different section better.
Enjoy your time in Houston......