well, honestly, I don't see such a big problem here. So, you have to teach your students the alphabet? Do it the same way you would teach it to kids, just adjust it a little bit so that it makes it fit for adults. Use more "serious" things to describe each letter, teach them the alphabet by heart etc. It consumes a big amount of time, but you have to do it.
When you finish they will know English better than their own language.
