What did your bitch die of?
You need a good formula for the puppies. It is probably good that they are a week old, they got the cholostrum from their dam, which should give them good protection down the line. At this point, the vet probably gave you some milk replacement formula?
Some people prefer to use goats milk and add some ingredients to this. Google milk replacement for puppies, goats milk, etc. I think it is better than the can of puppy milk replacer.
Has the vet taught you to tube feed? This is something that can be scary to look at, but it is a LOT quicker than trying to bottle feed 12 puppies. Make sure all the puppies are pottying on their own. I am not exactly sure when they start doing this on their own. Use warm water and moisten a soft cloth and clean the pup the way a mother would with her tongue, especially to make them potty and clean it up.
Keeping them warm, fed, and clean are the important stuff right now. If you do not have a heat lamp, get one and put it in a corner of the whelping box. If the puppies are huddled together, they are too cold. If a pup is off by itself, it may be cold. If all the puppies are laying apart, they may be a little warm. The box needs to be warm, that corner should be around 90 degrees. You can use a heating pad so long as it is removed before the puppies start teething on the cord and they can choose to lay on it or not.
What I did was to put the light over some towels in the a corner for my singleton. Then I took some bags of salt-fluid that they sent home with me from the ER and nuked them wrapped them in towels and put them under the heat lamp to keep a warmish bed for the puppy. she could move there or move off of there.
You need to feed those puppies often. The vet can tell you exactly how much by weight, and then how often. I am thinking at a week, they need to eat every 3-4 hours.