Gravity and lighting for an upside-down city above a regular city

Hello everybody,
on the attached screenshot you can see a rough demonstration of what kind of a city I am building right now. There is a city on the bottom and there is another one at the top of it. I’m going to be honest, I am better at modelling than unreal engine so I have a couple questions:
1 : How should I make the gravity?
2 : How should I use make the lighting? because I can’t add a directional light but I neither want the city to be always in night and darkness.

My ideas:
1 : I wondered if I could put in two directional lights one having effect only on the bottom city and the other on the top city. Is this possible somehow? And what should I do with the lighting of the building connecting the two cities? It would look pretty weird this way. Should I only use ambient lighting?
2 : The gravity should attract the player down to the nearest city’s floor but there should be volumes where gravity doesn’t have an effect on the player but I don’t know how to do it.

So I Found answers, and I post them here if someone needs them.

1.: The city should be in a constant night with only the light of the streets, buildings etc…

2.: You can create custom actor classes in c++, custom pawns and etc for the gravity, I would recommend for a similar project to create volumes which set the direction of the gravity and in some places (if needed) custom actors which attract the player in the direction of the surface normal vector.