Seller documents such as the Seller's Disclosure Notice and the Lead-Based Paint Addendum are assigned to Seller 1 by default. Once Seller 1 completes them, they are automatically assigned to the rest of your sellers.
Who is Seller 1 and who is Seller 2/3/4? It is simply the order they were added to the deal — the first seller you entered is Seller 1, the second is Seller 2. They are two distinct roles in Jointly rather than a list that reorders itself, so the position does not change on its own.
This is usually the answer to "why did the disclosures go to the wrong client?" — nothing is wrong, the two sellers just went in in the other order.
To change which seller completes them first:
Click the gear icon.
Select Edit Listing Information and confirm.
Scroll down, select the client who will draft the disclosures, and save.
The disclosures are now assigned to the selected party.
Reassigning the disclosures is done here, in the listing information, and only here. Editing the participant does not reassign anything — and it changes that client's name on every deal they are on, so it is not a way to adjust one contract. See How to Manage Participants and Contacts on a Deal, and Clients Sharing the Same Email if the client's email address is the problem.