In the process of doing this myself.
Firstly you need to sit and pass all 14 ATPL exams before you can go near converting the licenses. This can be done distance learning (what I'm doing) or in house in a few places. Honestly? I'd probably recommend biting the bullet and sitting it in house. You'll get it done quick and classroom really does help. Having the flying already done does however help with understand a lot of it, especially having done the CPL and INRAT exams. It's doable on your own like that with distance learning, but if time is an issue, classroom will speed it up.
As for the flying I'm told I need to do a minimum of 15 hours in a twin in Europe before doing the multi-IR as that's a requirement but I can't confirm this. Just the main hurdle seems to be doing the exams which is what you should get out of the way first, then worry about the flying etc. afterwards.
Haven't flown since July when I left Canada :/ Can't wait to get these finished. Good luck with it, hopefully that helped a bit, ask away if you want me to be more specific on anything.
Oh! Bristol for the distance learning says all the happy customers
