My favourites from your girls list are Sasha, Lara and Maeve - simple, pretty, good for all ages, familiar but not overused.
Second favourite would be Amelie (only downside is people hearing it as Emily)
Thirdly, Charlotte / Lottie - nice name but I’m not so keen on Charlie and there’s a risk your daughter would choose that when she’s older
Isabel - lovely but so overused right now (when you include all the spelling variations)
Beatrice - a bit story book as a full name and Bea is cute but not an “adult” short version for the workplace etc imo
Harper - not really to my taste but it could grow on me.
Boys:
My favourite is Sebastian, love this and it’s not too overused! Seb is a great short version.
Henry and Alexander are close seconds, just more commonly used than Sebastian.
Reuben, Conor, Patrick - all great too and not overused.
Jago - sounds quite trendy, different vibe to your other choices, it could grow on me.
Nice combos -
Henry and Lara
Sasha and Reuben
Conor and Maeve
Amelie and Sebastian (Milly & Seb?)
Charlotte and Alexander (Lottie and Alex)
Isabel and Alexander (Issy and Alex)
Harper and Jago