Problem:
Custom post type relationship doesn't show the right connected posts

Solution:
The problem with Views which show all of the posts of the related type rather than just the posts which are actually connected to the current post is because you are missing a Query Filter that specifies that only posts connected to the current post should be returned by the View query.

Go back to highlight the View block and in the Content Selection add a relationship Query Filter.

You can find the proposed solution in this case with the following reply:
https://toolset.com/forums/topic/custom-post-type-relationship-doesnt-show-the-right-connected-posts/#post-2299805

Relevant Documentation:
- https://toolset.com/documentation/programmer-reference/cred-api/#cred_save_data
- https://toolset.com/documentation/customizing-sites-using-php/post-relationships-api/#toolset_connect_posts

Problem:
Get product custom field data and save to order custom field

Solution:
Assuming that you are Toolset form's commerce then, Toolset Form's commerce offers the hook "cred_commerce_after_order_completed".
=> https://toolset.com/documentation/programmer-reference/cred-commerce-api/#cred_commerce_after_order_completed

With this hook, it has the product_id and based on the product ID, you can get the value of your custom field and it also offers the psot_id. So, what if you try to use the hook and based on the product_id get the value of your desired custom field and then assign it to your post based on the post_id.

Relevant Documentation: