how much fund need for gentral visitor visa from sri lanka

[ethan2017]

Hi,

I am living in uk and full time employee and married my daughters 1st birthday coming on august. i have 3 bedroom house.

I am planning to invite my parents (mom and dad) to that from sri lanka. they have around 4000£ in there accounts and have some lands in there names they are retired farmers. they don't have and regular income my sisters send money monthly but not regular when they want money they will send, they both visited Australia for 6 months two years ago and they are back on time and now in sri lanka.

They are planning to stay 1 month with me.

Is that fund enough and do i need to do something to this process

advice me please

Thanks in advance