I'm not sure how to develop my story idea that I've had for a year
I've had this idea for an entire year now and it's changed a lot for the better but I never really got to writing the first chapter because I kept planning, plotting, and wondering. Basically it's about four siblings (19, 17, 16, and 12) falling into a magical world Alice-in-Wonderland style - the same world their father disappeared years ago in order to find the soul of his late wife.
For a little background, the mother died, the father got obsessed with death and tried to bring her back from a dimension he believed was a Heaven-like state for the dead. He left his four children to the woman he remarried but their stepmother was quick to kick them out and had a child with their father's brother. They've been living as a working class; the eldest went off to war, 17 & 16 clean churches and aristocrats' homes, and their little brother is a part-time shoe shiner but studies quantum physics (cuz he's super smart duhhh) .
Still not sure how they end up in the other world but never mind that.
The teen siblings are separated by the magical world's unruly elements and forced to survive alone, finding different people along the way. The oldest 19, he comes across a band of soldiers; the 17 year old discovers her ability to summon spirits at will; the 16 year old befriends a werewolf .... because she genuinely has no friends. The 12 year old is captured by the witch/villain, who asks him to make her machinery for war.
It's really chaotic, I don't know how to develop my plot because I have 4 different journeys at once but I'm not sure it would make sense to combine them. 🙃 I don't know if maybe I'm adding too many characters, cluttering things up