If your premature infant has a sibling at home, there are a lot of things that need to be taken care of it.
There are different ways that you can support a child when their sibling is in the NICU. First off, make sure that you are spending one-on-one time with that sibling away from the NICU, away from everything else. For that sibling to know that they are still important, even though their brother or sister in the NICU is requiring a lot of time. That child still is important to the family.
Also, if your NICU allows visitation, make sure you are taking the sibling into to see the child in the NICU. You may want to wait until the child is off of the ventilator and monitors or whatever else so that it's not so overwhelming to the sibling. Let them go in and see what is happening in the NICU. They can understand the process that is going on with the sibling.
Many larger hospitals have child life specialists that you can have your child talk to about what they are going through and the stresses that come with having a special needs sibling. Another thing that you can do is make sure that you have a routine and schedule to their life. If they are going to other people's houses, make sure that it is the same one each day or each week, so they can have something to look forward to and that won't go away.