So sorry you're going through all of this. It sounds like you're doing the best you can and everyone would handle the situation differently. It's hard to keep a good home/hospital/work balance.
Our son was born with a complex congenital heart defect (diagnosed before birth). We knew he would be in the ICU until he was strong enough for open heart surgery. He he was in the hospital 30 days when he was born (25 days ICU). He had open heart surgery at 11 days and was on life support for 4. We were with him almost around the clock. We were at his bedside from 6am-midnight. We would go back to the Ronald McDonald House to shower and sleep a few hours. The nurses actually encouraged this. They said he would not know we were not there for a few hours and we needed rest to be at our best (I was still recovering from a c-section).
He had his second open heart surgery at 6 months. We did the same thing...stayed at his bedside from 6am-midnight. Once he was moved out of the ICU to the inpatient floor, one of us would stay all night.
My mom flew out to be with our 3 year old, I didn't work, and my husband had saved up 45 days of leave (military). So, work wasn't really an issue. My mom would bring my 3 year old in every other day (she would sit with our baby and we would take our 3 year old to the playground to play a little). I was difficult being away, but our newborn really needed us at that time.
Our heart baby is now 5 and had his 3rd open heart surgery this past summer. My mom traveled with us so there would be 3 adults to care for him around the clock (we slept/ate in shifts). My in-laws took our other kids for a month. Again, we felt our 5 year old needed us the most.
For us, we didn't know how much time we would have with him, so we were always there. But, spending that much time in the NICU/PICU, we realized we were the exception, not the rule. Most parents visited daily in the NICU; some we never saw. There was one nurse for each patient, so they got great care and the nurses would hold them, etc.
We became friendly with a family of a preemie. She ended up being in the hospital for 6 months! She's now 6 and thriving. She was/still is an only child and the parents had to go back to work. Mom would come on her lunch break and they both came every night/all weekend. Grandparents would help, too.
Just do the best you can. It is extremely difficult to do it all--nevermind the emotional toll it will take! If people have criticisms, just tell them you are doing the best you can--because you are.
You have no idea how long this will go on for, so you really have to prepare for a marathon--not a sprint. Keeping your jobs (and health insurance!) is important and so is caring for your other two children.
It sucks. It's hard! Hang in there:)