I had a small bleed at 6 weeks, before I had my 7 week scan to discover 2 heart beats. The bleed was most likely due to a haematoma visible on the scan, caused by implantation and was gone at 12 week scan. I only bled on one day for a couple hours or so.
Since I'd had a bleed, I was concerned that we wouldn't see a good scan (and also having a missed miscarriage previously). I think we were so relieved that there was a heartbeat to see, that there being 2 wasn't the biggest concern in that moment of finding out. Not knowing if the smaller one would last the distance kind of had us in limbo until 12 weeks.
The logistics of it all certainly are what is most overwhelming at present. I feel fortunate that my son will be 3yo when they are born, so I wont have to deal with toilet training whilst also looking after a really little toddler.
Good luck Mrswatto with the 3 children under 2! I'm sure we'll all work it out as time goes on. I got a booklet sent from the Australian Twin Registry, which I found helpful.