Is there insulation on the exterior walls? If not then that seems like the biggest/best single thing to do. I would bet there’s some way they can shoot in some without destroying all the walls but idk.
I don’t see how a mini split, which is generally less efficient than a typical outdoor unit, helps at all.
Spray foam insulation is another thing to investigate for the attic.
Also, and this is outside the box, what about planting some trees to throw shade?
Just realized I put “interior” for the exterior walls in the post. There’s no insulation. My parents tried the “non-invasive” spray insulation by a company but it bowled out some of the walls and outlets after expanding and really didn’t look nice at all.
We have 2 trees in the front yard already. One medium and one large. The large one is dying and I will eventually replace. The 3 large trees across the street do help for early morning in the meantime.
You can actually do noninvasive with blown in insulation instead of foam and that won’t cause your walls to bow. TBH that’s what I would do first, and attic insulation if you haven’t got any.