Hey Fiona,
Sorry I haven't poked my haed in to make some suggestions... but honestly, I can't. I have no idea! I am so sorry you are having some spotting etc. But I think I have heard that oyu can loose one twin and the other be fine! But I am not sure if you have to naturally (I know it's a horrible word) abort the second? I think this is something you Dr needs to clear up.
Good luck and I hope every thing goes well!

Tanya