I am interested in getting window films on several large windows to reduce heat from the summer sun. What brand would be good for this? Is this a do it yourself project or should I have it installed professionally?

Are the current windows thermopane?

Yes, the windows are thermopane.

I did my own and it ended up ruining the windows. The dark film caused the thermopane to absorb heat from direct sun light and the seals failed in both windows. Get 3 estimates from pros and see what they would do. Then you can benefit from their discussion of what can and can't be done. You can then pick the best bid or try it yourself.