Happy no twins in the family on either side! If they are non-identical (probably are as they have separate sacs/placentas) then there is no genetic link to prevalence of twins, so it will just be because two eggs were released. Chances of that increase as you get older (I'm 35). I was reading an article about this just the other day, weirdly. I did ovulate really late the month we conceived, and it crossed my mind that weird ovulation could mean more than one egg being released, but obviously never seriously considered there could be twins!
Spaniel in terms of symptoms, I've been very nauseous, which I was with DS, but it's been worse this time and I've also been throwing up, which hasn't happened before. I've been on medication for the nausea/sickness for 3 weeks and still taking it. I'm also massive already, but as it's technically my third pregnancy (DS and mmc previously), and my stomach muscles are knackered and I was still carrying extra weight from DS, I thought that was why. So I guess there were some possible clues, but nothing that couldn't happen as part of a singleton pregnancy.
Daisy they can't tell for certain yet whether they are identical. They seem to have separate sacs and placentas, so they are more likely to be non-identical, but some identical twins can also be this way (depends on when the egg split, if that's what happened, as opposed to two eggs being fertilised which equals non-identical). If they are different genders it will answer the question! But if they are the same gender, the only way they can be absolutely certain is for genetic testing, or to wait and see if they look alike!
Butter I would be so pissed off if someone else blabbed the news. It's really not on. It's your news and no one else's.
Welcome Sugar!
Cycling and Cloey congrats on the scans - such lovely news!
Wornoutboots I'm so sorry that you're still waiting for answers. It must be agonising. I really hope you get some good news at the scan 
Right, sorry for the epic post, but I think that's me caught up
. I've added myself to the spreadsheet and Super I will pm you about joining the FB group, if that's ok.
Off to bed for me.