when seller asks to stay past closing, how is best handled?

[Matt Berklacy]

in this transaction, my assignment of contract and original purchase/sale contract is already signed off by end-buyer, deposit is made by end-buyer, and closing set.

Seller asked, after the fact, if can stay 14 days free after closing. i asked end buyer, he verbally said ok, and he also offered monthly lease-back at fair rate to seller. Seller asked for addendum to contract stating that extention, and asked if i (assignor) and end-buyer sign.

Q. is a better solution, that buyer and seller sign a lease agreement stating 2 weeks free to stay after closing? And a month-to-month agreement set up to default after that?
(Q if separate agreement or addendum to original is used, is assignor (me) even involved or needed to sign anything at this point, as end-buyer already has assigned contract agreement of seller.)

any experienced, or settlement company, please chime in, in this supposed common scenario, thanks