Showing related records in a subgrid without adding them?

I have a bit of a unique ask. Try and bare with me as I do my best to explain what I'm after.

I've created a custom entity that is displayed on the Contact and Account forms.

If I add a record (in a subgrid) on the contact form, I'm wanting another subgrid on the contact form to display accounts that have a matching record, within the account record on a subgrid.

For example.

We add "Custom Entity Record 1" to Joe Smith's contact record in a subgrid. This "Custom Entity Record 1" also lives in a subgrid for Account 1 and Account 2. I'm wanting the record for Account 1 and Account 2 to automatically populate in a subgrid (or another better option?) in the Joe Smith contact record.

Any known ways to do this?

Thanks,

Matt