UK visit

[ang3l.in.paradise]

Hello,

My parents want to visit me in UK for a short time.
They want to sponsor their own trip to come here.

1)Can you please provide me a list of documents required by them in this case as its a self sponsor trip?
2)Do they need the flight tickets booked while applying for the visa?
3)Do they need the travel insurance documents submitted while applying for the visa? They are planning to buy it after the visa is granted.

please clarify on these points.

Thanks,
xxx