ERIN MCAULIFFE, 33, has worked at Merrimack Health’s Methuen campus – formerly Holy Family Hospital – for the last 10 years as a nurse in the maternity unit’s special care nursery. Both she and her mother were born at the hospital. In just a few weeks, McAuliffe will deliver her first baby there as well. “This birthing center has been a big part of our lives. It’s something that is important to our whole families,” she said. But on April 1, the …