So I didn't find a simlpe and quick way to do this, but after a lot of research this is the best I could do. This is an example of what I wrote on the child models.

@api.onchange('location_id')
def _onchange_location(self):
    for r in self:
        r.parent_id.update({
            'location_id': r.location_id,
            'product_id': r.product_id,
            })
        r.parent_id._onchange_location()

I had to manually update the values of the used variables in the parent model, since they weren't registering with the new values when the onchange function was called. I had to use `update` instead of `write` because the latter was causing double calls to the database and double chatter messages on tracked variables.