Final weeks of flowering

This is my somango xxl plant about 6 and a half weeks into flower. is there anything I can do about the leaves turning yellow. Is this normal should they be this yellow ? And should I rip them off. Also this is my first grow. Any tips on harvesting and when to do so

The yellowing you are seeing is your girl(s) closing in on her end of life. As her flowers get closer to "ripe" the plant focuses less on chlorophyll production, and more on trying to get pollinated. Your leaves lose color but your buds swell up. On your close up there is a little damage on the fan that I may have questioned, but as close as you are to finishing I wouldn't worry.
As far as harvest, get a magnifier, min 30x, 60x is better, 100x is best, any stronger is overkill. Your trichs are your most reliable indicators. They start crystal clear, then cloud up as it matures, and finally turns a golden amber color. When your trichs are roughly 95%/5% to 90%/10% cloudy to amber you are in your prime harvest window. I start watching my trichs when about 90% of my pistils/ stigmas have changed color and receded back toward the calyx.

Also don't focus so much on the time frame. This sounds worse than it is intended but, she will be ready when she's ready. Keep track of the weeks for general tracking but don't try to base your harvest on time, you'll rob yourself. I've had it suggested to put her in the dark for 24-48 hours before harvest. I'm not experienced enough to know if the is any merit to this.
Back to trichs, I start my pure water flush when her trichs are roughly 50/50 clear and cloudy.

It doesn't look like fade to me, it looks like some kind of lock out. Nice buds forming though.

Its most likely normal if they're mature. Its very normal for this to happen at that stage.