Visitor Visa Fund Requirements

Hi,

I am planning to invite my parents from India to UK on visitor visa for 3 months. I am sponsoring their entire trip (including travel, accommodation and personal expenses). They will stay with me in my rented flat. Given this condition,

1. what should be the fund balance my mom and dad have in their Indian bank account for successful visa process?

2. What should be the balance I should show in my account to support their 3 months trip for successful visa?

3. Also, is there any conditions on sponsoring accommodation? e.g. they should have a separate room,etc?

Your help would be very much appreciated.