Seller refuse to vacate after settlement

Hi guys,

Hopefully I can seek some advises from here.

So apparently I've bought this house from this divorced couple and they have already signed the contract and settlement booked.

At the beginning it was a bit difficult to get the lady (she is in her mid 60s with depression) to sign the contract but after some hard work she agreed.

Now my settlement was supposed to be this friday however, my solicitor just tell me that the lady has spoken to her solicitor and ask if settlement can push back to the 1st April, and MAYBE she will settle.

During my communications with the agent I've been told that the lady was very difficult to dealt with and that she kept changing her mind and refuse to leave.

I've told my solicitor that I will be issuing the lady a notice of complete on Monday due to her failing to settle on time.

Now my question is what are my other options if the lady still refuse to leave after the 2 weeks period granted from notice of complete?

If I am to forfeit that property and look for another one, I've been told that they will need to pay for any difference in price due to my lost of opportunity? So how does that really work?

Thanks guys
I have been studying law for 2 weeks and as your solicitor I advise you to serve the vendor a default notice which gives the vendor 14 days to remedy the breach. This will cost you $440 and the offending party will be liable for all legal costs. You cannot eject the vendor unless issue this notice after settlement crashes and wait for the court response
Sincerely yours
J Cochran