For funsies, let's say DS1's name is William. Would naming DD something that ends the same, like Miriam, be strange and too rhymey? FWIW, DS2 will have a name that sounds nothing like either of these. Will he seem like the odd one out?
Also, I *may* be BNC (baby name crazy).
Re: too matchy for sibset?
Eh, it might be too close.
And we welcome the BNCs here.
1/12/13 DD was born
4/9/16 DS was born
9/17 CP
6/23/18 BFP EDD 3/4/19
This. I knew someone named Elliot (boy) and he had two younger siblings (who were not twins, but even if they were, it's still awful) named Olivia and Oliver. Your sibset is not as bad, but I wouldn't do the William and Miriam thing.
They are close enough to sound fun together without being silly [Like sibset Oliver and Olivia] or being deriviates of the same name.
Besides, the nick names for both are so different that unless they are going solely by their full names I don't see it being a problem.
And in regards to DS#2's name being different, I don't think that should be a problem at all. In fact I think it's better that it isn't quite so close to the others.