How can I fix the problem with the sunlight coming in triangle windows

Add window treatments, be it curtains, blinds or even window film.

use privacy film

I got the non-adhesive window film, you can get the one-way reflective type where you can see out but it reflects heat and UV rays out.... https://www.amazon.com/Window-Daytime-Privacy-Mirror-Silver/dp/B00CWGIHBE/ref=sr_1_cc_3?s=aps&ie=UTF8&qid=1527610172&sr=1-3-catcorr&keywords=window+film+one+way+heat+reflective does come in 4 colors.... silver, bronze, gold and black

https://www.amazon.com/FILMGOO-Privacy-Control-Anti-UV-Non-Adhesive/dp/B07CYY5NSJ/ref=sr_1_cc_6?s=aps&ie=UTF8&qid=1527610172&sr=1-6-catcorr&keywords=window+film+one+way+heat+reflective

there is a reflective film available you can apply with water & a squeegee- you can see out but it reflects light & heat away -

There is a film that you can purchase that filters the light coming in

Try some film that blocks heat but not view!

https://www.homedepot.com/p/Gila-36-in-x-180-in-Titanium-Heat-Control-Window-Film-HRT361/100616385

I have the same windows in my kitchen! You can use a film that you just apply to the window like contact paper!

you could also use that liquid crystallizing stuff for glass fish tanks.

Do they even still make that stuff?