Documents for standard visitor visa

Hello,

Apologies if this has been asked before. I will really appreciate your valuable inputs
My parents are planning to visit the UK and will apply for a standard visitor visa.
We had some queries:

1) Do both of them need to make separate applications?
2) They were here for 2-3 months each in 2013 and 2015 - after that, they are planning to visit now. Will there be any issue if they plan for a 5 year multi-entry visa - how can we make our case strong here?

Regards,
PB

1) yes.
2) advice.

Thank you

When the appointment is made, is there a way to link both the applications?

Hello,

I am planning to get my parents to uk on a visitor visa.

They own a couple of houses in India.

What documents should be provided as proof of ownership of the houses? - will a society letter do or is something else required?

Thanks