Check valves are a excellent idea, regulators don't do well when full of ale. The best way, as suggeted above, is to have a manifold with built-in checks. Since you already have the 4-way spliters, one check valve per line is the best. If you have any tubing between the regulator and the splitter, you could put one valve there, at the risk of ale blowing from one keg into another.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk