How can I capture two addresses per item solf

I am trying to provide a service that would ship one product to two locations, first to the one location, and then to the other. 

Example: An embassy has my customer's passport. The embassy requests that we send them a prepaid envelope so that they can return my client's passport to them. I need to prepare two envelopes. Envelope1 has a label addressed from me to the embassy and contains Envelope2  which is addressed from the embassy to my client. In order to prepare these envelopes and labels, I need the address of the embassy (address1) as well as the address of the customer (address2)

The point that I am trying to make here is that I require each sold item to capture two addresses (the address of the embassy and the address of the customer). I have two questions about this situation:

1 - What is the best way to capture the addresses? I am considering both Custom Checkout Forms and Form Blocks. The Custom Checkout Form seems neater because it has built in functionality for an address, BUT - based on this I believe that the Form Blocks capture the data in a way that would allow Shipstation to pull the data, which would be extremely useful for processing the order.

2 - Is there a better way to achieve this? PirateShip might have better integrations, but it requires Squarespace's Advanced Commerce plan, which I have no use for.

I would appreciate any thoughts or insights about this. If possible I would like to avoid code, but I am open to that approach if necessary.

@paul2009 you seem to be the expert in this super-niche topic. I would really appreciate your help if you're still active on this forum.

14 hours ago, Aardvark said:

I am trying to provide a service that would ship one product to two locations, first to the one location, and then to the other. 

You can capture the customer's delivery information via the checkout (as normal) and capture additional information with a custom form. However, your shipping and workflow processes will need to be managed manually, off-platform.

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