Most Kawa-compatible licensing scheme for a new project?

[spellcard199]

Hello. I'm writing to ask an advice about the licensing scheme for a
new project in which I may include code copied from Kawa and then
modified by me.

I can only imagine 2 scenarios, but I don't know :
- if my understanding about the 2 scenarios is correct
- if there are other choices besides them

Scenario 1:
1. I distribute my project under the MIT - Expat license
2. Since I've choosen the MIT license, I can't include code
   that I have modified after having copied it from Kawa

Scenario 2:
1. I distribute my project under the GPL license
2. Since I have choosen the GPL, I can include in my project
   code that I have taken and modified from Kawa
3. Let's say that someone in the Kawa team at that point wants to
   copy->paste->modify some code from my project into Kawa: since Kawa
   is also MIT licensed, would the fact I used the GPL forbid this?

I'm asking because I'm trying to write a java project to support
interactive development in Kawa (porting my own `geiser-kawa'
from scheme to java atm) and, in the remote case it's decent,
some functions may happen to be reusable in the Kawa Language Server.

So my question is: what's the most Kawa-compatible licensing scheme
that allows both of the following?
- Code from Kawa to be copied->pasted->modified into my project
- Code from my project to be copied->pasted->modified into Kawa

Thank you in advance for the attention.