Maybe increase the pay so they aren’t searching for another job when they are forced to retire at 56 without training for another career. And also decrease hours needed to work per week to account for the additional stress they face so they can recoup. You would surely have more people applying when taking these factors into account.

Sounds like they need to increase pay and reduce the number of hours worked while still getting a salary and benfits to entice more people to the position and make the stress more bearable for those they can get to fill the position. It’s not a matter of how many people are qualified it’s a matter of how many people want to make the tradeoffs to work there and be upskilled to meet the requirements. If your deal is not enticing enough, you need to restructure how the position works in order to entice more people for the position.