I am reaching out with a suggestion that some may have suggested but I have not come across. Speaking with an assistant online I have been told it is a bundle SKU. Best way I can explain is the following:
Child Product SKU A
Parent Product SKU B
Parent Product SKU C
Both parent SKU B and C have a component included within called Product SKU A (Standalone or child). I do feel shipstation very much have the infrastructure for this but as soon as we include a standalone product as a component to a second parent SKU, it simply transfers the SKU A from say Product SKU B to product SKU C but will not apply to both. This is very handy if you have a parent product built with components and sell those components individually. Suppose like a tool kit, Parent would be the complete kit and suppose some customers are after replacement you can track the inventory but likewise these individual tools can also be part of another tool kit.