Good luck. It takes lots of patience and sleepless nights! I've done it a few times - successful and unsuccessful. I tried all of my 4 (two attempts) and both failed. So in the end I just listend to them and kept them as two separate pairs.
My advice is to keep a spray bottle of water handy, although now its getting colder it might be better to just use a long sweep brush. You use this to separate them when they are fighting/latching on too hard. You don't hit them or use it aggressively just gently to separate. In my experience just that something coming next to them makes them separate.
Any blood shed then stop the bonding as thats a really bad sign.
Get lots of cushions for you to lie on as its good to stay close.
Good luck x