Timeline Rollup integration/configuration
The relationship "Customer" is a special field that indicates either an Account or a Contact. This creates a bit of confusion for the rollup concept.
I suspect you need clarity around the actual hierarchical relationships so that they are setup as Parent -> Child -> Grandchild.
In general I would not expect a "Contact" (aka a single person) to be the parent of the records, it might make more sense to configure Account as the umbrella entity.
Your second choice is to consider the spider web of the relationships and configure a different approach to rolling up data. The system will need to understand, very possible you can get around some of the "traditional" using some of the newer AI features.
Cheers Anne