As a father, what can I do to make my daughters happy if I'm working abroad?

I think that you should try some of the awesome communication apps that are available nowadays. A lot of kids aren;t too interested in a simple phone call anymore, and with things like Skype and FaceTime available can you blame them? You could try one of those for nightly conversations. Or you could get WhatsApp or Viber for quick and frequent conversations. There are so many great options nowadays that you won't have to feel far from your daughters even if they are elsewhere.