Ignatius is one of my top favourite names too, I just love it.
It's so classical and yet very interesting.
From your suggestions for the siblings' names, I like:
Ambrose,
Cedric,
Remus,
Caspianand
Arabella,
Constance and
Minerva,
so pretty much all of them ;).
I think you've a great taste, I love the names you love lol.
A few more suggestions for names for
Ignatius' siblings:
boys
RufusIainFidelio
MiloWilliamFinnianFindlay,
FinlayPhineasSiriusSilasWilburTheodoreHoraceHenry
girls
HannahOlivePaulina /-e
TheodoraEmmelineGeorgetteFinna
WilhelminaVioletWilmaTovaBrionyBethAvelinaAimée
OpheliaClementine