Bridesmaids | Groomsmen

what about something like this? You could put your groomsmen in a button up (either plain white or a subtle print like in this photo) and do some kind of neutral/earthy or even khaki coloured pants, suspenders pictured but that would be up to your personal preference. I think it works here

I think what you are planning to do is beautiful! I am planning on mismatched bridesmaid dresses as well, and this is one of my photo inspos on pinterest :p

The groomsmen, I might add just vest or something simple to differentiate from your groom, depending on the formality of your wedding the groomsmen could just wear their button up as well, since you are not doing ties/bowties! I wouldn't mix black and grey in my opinion though (too much mismatching with the bridesmaids already doing this)

Charcoal/grey is so much more versatile and in my opinion looks better than black unless you're going full tux or something. I also think you should reconsider navy. It would look so nice with your bridesmaid dress colours!

I think white shirts will look nice with any option.

This is my personal preferences based on menswear, so take it with a grain of salt, and of course feel free to use or not use any of the ideas.

If you're going the casual look, I suggest charcoal or grey over black. Not only is black a super formal colour, it'll also burn your guys in the August heat if you plan on doing anything outdoors. And with black suits, your guys will have very little use for them after the wedding except funerals (black suits aren't used for work other than security guards and limo drivers lol).

Charcoal won't contrast as hard with the white shirts and will compliment most skin tones better than black. They also look better in photos.

You can coordinate the groomsmen with the bridesmaids with a pocket square. They don't need to match exactly but an assortment of blush/earth tone pocket squares would go nicely.

I know you said no navy/blue shirts but what about a dark navy suit? They're also very versatile and can work if you want to incorporate some of the pink or blush into your guys' ensemble.