My sims can't pass through that narrow passage either. I've also had 2 issues in Tuatha's Garden with similarly tight spaces. I don't recall if zenport works in the China tomb, but in Tuatha's Garden there's not enough space past the restrictions to zenport to. Like @IreneSwift , I also use the testhingcheats teleport option to get past this part.
I once tried fixing it in build mode by making the passage larger, copying the lot to the bin, and using that to replace the original tomb in new games. But then later quests in that tomb were broke. So I went back to just teleporting with the testing cheats. There's no other way in.
