The Eldest are actually very close, you will often find both sisters spending time with their "little" brother.
Personality wise:
Luca is the Leader and has inherited her Father's calm rational personality... and his affinity for crushing things. she often will accompany her Father and Uncle Luna in "preparing" planets for her Mother to eat
Ember is more care free and had actually a bigger appetite then even her Auntie Suzzanne, luckily for everyone she loves making her meals last longer by shrinking down to 5 ins (120 cms), but could eat an entire Universe and still have room for dissert.
Nova actually is the most Mellow of the 2 and actually has a Surfer vibe to him, although of the 3 he is the one who inherited Anubis and Blaze's absolute love for Battling, he often goes to Planets in the pantheon where the Pokémon are at his proportion and will Utterly clean house in their battle circuits.