What kind of wax is used in the tea light candles that come with it? 
Palm wax, they are also 70% Palm oil. 

Are these tea light holders reusable? How long do they last? 
They are completely reusable! Once a tea light is burned through, you can simply take it out and pop another one back in whenever you want! 
They last as long as forever, unless if you drop it and it breaks. 

Are the tea lights scented? 
I am currently using non scented tea lights. But you could always put in your own scented tea light. They fit any general sized tea light. 

How long do the tea lights burn for? 

The tea lights from that I use have a 4 hour burn time! 

Does the resin emit fumes or melt when the candle is lit?
No, the resin does not melt or emit fumes! It has the tin from the tea light, and the glass from the holder as a barrier between the resin & tea light.