The first bug is because of the second, both pretty easy to fix.
One solution would be to add a bool input to the Increase player mana interface message called something like bIncreaseMax, then in the implementation in the player state you can then add a branch which will also increase the max mana like you have described.
You will need to change this for both the player state and the player character (AI version of the player state) if you wish to use the AI that comes with the toolkit.
Hey SaviorNT, the toolkit takes advantage of Unreals multiplayer framework. So the setup and support for this would be limited by the engines ability to provide this, which thankfully it does. I have not personally tested multiple mobile devices on ad-hoc wifi, but setup with the toolkit should not be to difficult, or if any additional work is even needed. So In theory it should work out of the box once you deploy and have the same* version on both devices. Hope this answers your question.