Getting to and from Malta can be a pain, and can involve major detours. I was there for a conference a couple of months ago, and one of the delegates came from Crete - straight across the water - and he had to fly all the way to Milan and back down again.

Getting to Tunis... your best bet may be to travel by ferry via Sicily:

This site

http://www.directferries.co.uk/tunis_ferry.htm

lists ferries from Sicily to Tunis.

I know there are ferries between Malta and Sicily as I saw them being advertised when I was in Malta, but I don't have any details.