I actually quite like Mackinlay - spelling: Mackinly, Mackinley, McKinley? But I also like
Carson too! I think
Carson goes best with your boys and it doesn't matter that two end in "-son"
I don't really like
Matea - my sister (definitely not name-nerd material) looked at the name with a confused expression. She has no idea how to pronounce it and if I'm honest I might stumble to get it correct too. Maybe use it as a middle name if you both like it?