On the topic of siblings, I would prefer them to be younger, simply so they can be another Barry-like character who's always saying their going to be the best trainer, yet they never seem to win against you. Plus, they'd be the comedic character in the game like Barry was portrayed to be - and impatient too.
Yeah, I like Barry, so why not have someone similar, right?
Going with this idea though, because the protagonist is now older, I think it could work well with your younger sibling getting to choose one of the region's starters.
As for the parents, I would love to have both a mom and dad please. The dad could be a Gym Leader like the father in RSE was; I thought that was a pretty cool twist compared to not having a dad at all. As for the mom, I'd like for her to be the bank again. I found this so useful in HG/SS, saving a lot of money and getting some when I needed it. However, I'd also like the mom to interact with the player as well. DPPt did this a bit with Johanna, but not enough I think. So, if anything keeping the parents appearing every now and then (along with your sibling rival) would be a great addition to the story.
May I add to this, but I'd like another rival as well, one who's quite tough against you with a great line-up of Pokémon, strategy, and is about the same age as you. This character however will not be part of your family, but instead hopefully take part of the plot in the game instead.