If one of your babies has died, it can be an extremely difficult thing to deal with the internal conflicts that can arise. Grieving for one baby and feeling unable to be happy about the other baby(s) that survived, or struggling with newborn mothering while grieving for your dead baby are some of the complex emotions you can be faced with. Being told 'at least you have one (or two etc) live babies' can be very hurtful, as if the baby that died was not important.
Take your time, all these feelings are normal. Allow yourself to grieve for your child and say goodbye to them in the way you want to. Perhaps organise for your living baby(s) to be cared for at certain times to give you the space you need to grieve or spend time with your dead baby. You love all your babies, they are all important and it is essential that you acknowledge your grief.