[tmerr]

My advice:

Tell the teammates that you want to see them grow to become code reviewers. At first require PRs to be approved by two people: first someone else reviews it. once they LGTM, then you review it for final approval. Do this for a while, until you start noticing like you have little to add. And then grant the relevant reviewer the privilege to review in a single pass. Bus factor += 1, and better knowledge transfer.

That is the process you'll have when you get back. But in the short term, it's probably fine to let them approve each others code while you're gone. Yes they might they break something.. but you can always roll back (I hope). Blocking all PR merging until you return sounds a little overkill to me, but there might be some reason the stakes are so high that I'm missing.