This may sound kind of stupid to most people here, but I haven't a clue, so I have to ask. 

I've got an old Harry Potter set that has the steel EZ Tracks.  My grandson just got a set that uses the nickel/silver EZ Tracks.  Can the steel and nickel tracks be combined to enlarge the present layout?  Also, can two engines be run on the one transformer?  If not, is it possible to double up transformers?

Thanks in advance for your help.

Rick