Do python games use Lua?
Is it a resonable thing or I should just stick to pure python?
Python has been used in many game development scenarios. While Lua may be well known among some game mod circles (like WoW GUIs, Garry's Mod, and so forth), Python was the language of choice for Civilization IV modding. So it's not like the language is unknown among game modders in general.
If the people working with you don't know Lua, then a larger question is this: why aren't you writing the engine in Lua to begin with? I mean, if Lua code is going to be faster than Python code due to JIT, why would you not want the entire codebase to be in Lua?
It's strange that you've gather together this group of Lua programmers to make a game... in Python.
If you're doing it that way because Python has access to modules that Lua doesn't, then I would suggest using your Python->Lua bridge to give Lua access to those modules and let your Lua scripts do most of the heavy lifting. You'll be able to use the rest of your team as more than just game scripters. And Lua already has plenty of mechanisms for encapsulating scripts, so there's no trouble with sandboxing AIs from the rest of the engine.
That is, write a thin wrapper around your needed Python modules, expose it to Lua, and transfer most of the engine into Lua script. From there, use your Lua scripts to execute potentially user-scripts as needed.
However, if you don't want to do that (presumably because you don't want to code in Lua), then you can stick with your original plan. There's nothing wrong with it per-se; it's just odd to have a script-based engine call a faster script-based scripting system. Generally speaking, it's the core engine stuff that needs performance the most; the AI scripts don't need it as much.