Hi and welcome back!
I'll try my best to figure out something for your dergs :)
This is what I got for Yoake:
Cinder/Blaze/Stained
I wanted to stick with him being a Guardian, but I had a hard time with his Platinum secondary, so I changed it. His eyes don't match his colors that well, unfortunately..., but I think he looks pretty nice otherwise.
Soleira was a tugh one mostly because there's a lot of different opitions for a XXY (white/white/some other color), it all depends or what you're trying to achieve!
Boulder/Myrid/Soap looks kinda nice...
Piebald/Paint/Koi looks... interesting?
Maybe just... make it sparkly?
Sparkle's often a good way of dealing with problematic tertiery colors... or a way to incorporate them into the design. Purple apparel should make it more fitting than just a slap of color on a white base :)
When it comes to your 5 year olds...
Orion, honestly, is a great looking dragon as he is. Personally, I would chance the Runes tertiary for something more subtile, like
Sparkle or
Firefly, but it's not necesarry if you don't want to grind! You can give him some apparel if you want tho, I think it will help make him look more interesting :3 His eyes match his secondary color really well!
For
Theseus I got this proposition:
Iridescent/Bee/Filigree
I love the array of light, pastel colors white Iridescent brings with it, but I'd say a gray-ish secondary isn't the best choice. I'd try to use Bee gene to lighten that dust secondary and maybe throw some Filigree to the mix?
(For the love of Windsinger, I hope I didn't make a lot of typos...)