I found an add-in that apparently will do this sort of thing though I don't know if it will then work on your iPad.

http://xongrid.sourceforge.net/

I used their function INTERP2DTAB. I tried it and could not replicate for your data how it worked with their examples. I keep getting "Error: Duplicates".

At any rate, this is going to take some doing likely using OFFSET functions and am afraid I may be out of my depth on this. I'll keep trying.