I think you are missing to big picture here. You bought a house based on them selling a house with a pool and no material defects. That’s fraud. It’s not up to you to resolve it- it’s up to them. That home with the damaged pool disclosed would not have sold for Anywhere near what you paid-guaranteed. So , in essence, they stole from you.
call your lawyer now. Right now. Not after you think it might be repairable cheaply or not. Not after you determine why it failed. Why it failed is immaterial to the issue. They lied and covered a substantial know defect and are now liable for damages To make it right. Once they are on notice, then you can go about establishing the whys and how much. Even if it’s the neighbors fault, it happened before You bought the propertymso they would need to sue the neighbor Not you.
The lawyer will guide you through the steps needed to gather the evidence to prove in court they knew. They will also determine the sellers ability to pay. Once those are known, they can provide the possible range of options for you to consider (fix it yourself and place a lien on their new home, void the sales agreement and move out, attach their wages, etc). BTW if itmcan be proved that their RE knew, they will lose their license too.