Wow, this is a dilemma. What does your agent say?? We get lots of questions on this forum that could be answered by the buyer's agent, if they had one. Do you have your own agent??
If not, I agree with my New Orleans colleague here, I don't know the rules in your area. In MN, the seller automatically gets an additional 30 days past the first closing date if they need it to deliver clear title to the buyer. Beyond that, the buyer has the option to cancel the purchase agreement or can let it go for a time period to execute a statutory rescission.
How long has this been going on?? You may want to consult an attorney to determine what your recourse is here. If you're losing money (higher interest rate), then, every time the seller requests an extension, you can negotiate a fee to come from them for your hardship.
Again, I ask, WHERE'S YOUR AGENT?????
I have never once had a seller hold up a sale.. So fill in the HUGE blank of why the seller is holding up the sale.
Generally speaking you would have to agree to the contract extension as well.