Wedding colour theme needing help

There's no law that says everyone has to coordinate anyway, so if you want those dresses, have them.

If you want it to look more coordinated though, you might find that going for a darker, bluer tone in the dresses would help, to blend in more with the blue stripe in the tartan.

Alternatively, if he's hiring his kilt (or buying a new one) then he could pick one of the lighter Stewart tartans, but appreciate if he already owns a kilt, it's not economic to get a new one just for the wedding!

Hi! Exactly as the other person mentioned, your day, your rules and choices. But I also understand wanting that picture perfect color combination. So maybe keep the dress shape but change the shade? Or the color? Is any other color attractive to you? Maybe burgundy or deep purple? Or perhaps forest green?
Any choice you make is great as long as it makes you happy.