Hmm. Let me see if I can fill in some more details.
The emotional exhaustion comes from all directions. First, bear in mind that most multiples are premature. That means the parents have probably been spending hours and hours with their babies in the NICU long before they can come home. Depending on the condition of the babies and their birth weights, they could face hospital stays ranging from weeks to months. That is expensive and emotionally draining. Every day in the NICU is a roller coaster. A baby who is doing well in the morning could be near death's door by evening. Things change that fast.
Also, it's quite likely the babies won't all come home at the same time. Again, it depends on their progress. So that means Mom and Dad may be juggling the care of one or more babies at home AND making daily trips to the hospital to spend time with the other babies. Someone has to drive Mom because she isn't allowed to drive and is in too much pain. She may not even be strong enough to ride to the hospital, so the burden of visiting babies there could fall entirely on Dad. But Mom would still need help at home while he is visiting babies in the hospital. She's going to need help feeding, changing diapers, tending to monitors, as well as her own self-care for bathing, eating, etc.
Most newborns feed approximately every 2-3 hours at first. This means massive sleep-deprivation. Preemies who are underweight will feed every 2-3 hours for an extended time frame. Mom can't possibly breast-feed four babies, but she may be pumping breast milk. And she will be using formula (probably high-calorie to bring up the babies' weights) too.
The support network could be free or inexpensive for a short period of time but not for more than a few weeks. After that, the parents will need to muster friends, family, church members, etc., to step in and help out. Yes, this support network can be intrusive and not always that much help. Think about the people with good intentions who are uncomfortable handling a small baby or who are reluctant to check monitors or who fix food Mom can't eat or leave lots of dirty dishes after fixing a meal.
Body awareness and sex are probably the last thing on anybody's minds, including the Dad, who is probably stressed about his wife's health, finances, and the welfare of his children. It's not that the parents no longer love each other, but they are overwhelmed. Imagine this environment in your home:
Four-to-ten strangers or relatives taking charge of everything, including food, cleaning, errands. None of them do things the way you're used to. You have no privacy because someone is always there.
Sleeping no more than two hours for any given time.
Crying babies. Alarms going off at random times.
Hospital bills rolling in with numbers ranging in the hundred thousands.
A boss asking how long you plan to be off work (for the dad). Worries about using up family leave. Worries about taking care of the wife, the babies at home, and the other baby+ in the hospital.
Constant questions about health issues with the babies: Why is this one spitting up all the time? Why has this one lost weight? Does this one have jaundice again? Shouldn't they all be growing at the same rate? Do we need to take this one back to the hospital because she/he is listless, crying, throwing up, etc.?
When do things get better for the couple? When the kids are stable, the mom and dad have a routine that works, and the mom's health is back. Not before. Best guess is at least several months.
Could the mom take extreme actions if she or her family were threatened? Probably. But it wouldn't be easy, and there would be a price to her health. She could open stitches, develop post-pregnancy complications, or injure herself internally.
Hope that gives you some more insight.