Nice family-oriented storyline possibilities here, too.
To help you work though the story line and to help clarify things in your head, why don't you write an essay ... 10 pages tops.
START ... write the family backstory (read my article
BACKSTORY BASICS for some thoughts on that). Having the backstory will help clarify who-gets-what-issues, behaviors and perhaps why the characters act the way they do.
STEP 1: Outline the essay on 1 page.
STEP 2: Rough out the essay itself ... just get it down, even badly ... on paper. If you know something needsw to happen, but you're not sure what ... put a "placeholder" in the essay, like: (PUT MARRIAGE BREAKUP SCENE HERE.) You can come back later and work it out.
STEP 3: Re-write the essay for clarity and to add more details.
STEP 4: Re-write the essay to its proper length ... 10 pages, no more.
STEP 5: EVALUATE ... is it visual? Does the viewer/audience learn something from what happens to these characters? Can we identify with them? Do we care about them? Who's the "bad guy" in the story?
STEP 6: Polish up the essay to add nuances you discovered in Step 5.
STEP 7: Write a logline ... a one sentence description that describes the movie.
STEP 8: Find the 20 major scenes that take place in the story and put them on 3x5 of 4x6 cards.
STEP 9: Write a rough draft of the movie script.
STEP 10: Re-write and polish the script.
This will give you a structure to start form scratch and get something down on paper you can work with. That's often the hardest part. You can do it ... you just have to start!