Congratulations OP, twins are fab, don't let anyone tell you otherwise.
Some great tips here.
Routine worked for me too, DTS2 was in SCBU for 2.5wks and they got him on a strict feeding routine which we started DTS1 on and we managed to keep to when we got them both home. We also always woke the second baby immediately after feeding the first baby, it meant you got a longer block of sleep.
Two bouncy chairs/swings are essential IMO.
Definitely get visitors to help with washing/sterilising/cooking/bringing food if at all possible. Best of all, get them to play with your older child.
Find your local twins club now and go and visit before your DTs are born. Your older child will be used to it and you can get valuable advice. You might also pick up some second-hand bargains.
Online shopping is your friend, especially with 3 children. If you want to venture to the supermarket, it is worth checking out which ones have suitable trolleys as a lot don't have many twin trolleys, let alone ones which will fit 3 children in.
If you can, get your older child interested in dvds/tv programmes and save them for feeding times so he/she is occupied for a while. If you have sky+, record a few episodes of his/her favourites. 19 months may be a bit young to be using the remotes but it won't be long before he/she can do it herself.
If you can afford it, get a cleaner to come in once a week (at least for a while). Also, it might be worth investigating nurseries/childminders for your 19 month old to give you some respite, even if it is only for a few hours a week.
I also found getting out of the house every day, even if it was just for a short walk saved my sanity.