HELP! alteration to contract seller wont settle!

HI thanks so much for your help before everyone on late settlement penalty interest. Now i have come to a new band. I gave the sellers an extension of three weeks because their banks wont settle something to do with them trying to discharge part of their home loan. Now itis supposed to go through on fri, but the real estate coimpany are telling me it looks like it wont go through on fri either. They want me to sign a variation of contract sheet changing the date till fri. Should i do this? And have now said i must give fourteen days notice if i wish to terminate the sale, because now i have had enough. I am so stressed and it has cost me money in insurance and taking time off work and ahhhhhh it is so stressfull!! Soo if i decide i don't want this anymore should i not sign the contract and just give my 14 days notice or do i sign and give 14 days notice. If you change the contract do they get three days grace again??? If the house settles within that 14 days notice do i have to legally buy it? OOO soooo many questions from a ditsy first homeowner who decided to do their own settlement. Never again . Please help!!!!