I cant find isomalt to use, but i would like to do the corals. Is it possible to substitute with ordinary sugar, then colour it and pour over ice?

Yes you sub reg granulated sugar. Especially since you are coloring it. Isomalt stays clearer then sugar, but since you can't get it. Use the sugar.

I am going to use the sugar to make the coral. I dont have the isomalt, so can anyone explain the technique?

How cool must the sugar be before i pour over ice and which is the best colouring to use i.e powder or liquid or gel?