Visitor visa clarification

[gopugopu]

Hi Experts

I am planning to invite my parents for 3 months in UK, I have below questions if someone can answer that will be a great help.

My father works in a factory, owns his shop and have some agriculture income (all stated in ITR) and my mother is house wife.

1. My father works for a factory and he is paid in CASH monthly every 25th, his pay slips states that "paid in cash". Paying in cash, is that a concern to HO why salary is paid in cash and not directly to bank account ?

2. Factory's accountant is willing to give a covering letter that my father works in the factory, his salary is paid in cash and has applied for paid and unpaid leaves and upon return will join the factory again, is this OK or does he needs anything else ?

3. My father does have decent savings(FDR's) and property in India for which he will be providing proofs.

4. His bank statements shows that lump sum amount is deposited every month, though the amount is not fixed (varying between 22k-35k INR) as he has other sources of income as well, all sources of income is written in his ITR. He will be submitting ITR for last 3 years.
Does he need to take any other steps here ?

5. I will be submitting all proofs from my end that I will sponsor their trip(cover letter, bank statement etc).

6. In worst case scenario if their visa gets rejected for any x,y,z reason can it impact my ILR application, I will be submitting application for my ILR in November.

Thanks & Regards
Gopu R