The fact that your income exceeds the LICO threshold does not matter for for your parents' TRVs. - Thank you for the confirmation.
Do complete the eligibility questionnaire again. It would ask if you want to submit an application for another family member. - Sure, I will check that again
One online account, two applications. Your dad will be the principal applicant. - Yes, I also want him to be the principal applicant
If she is paid through checks or bank transfers then that is evidence of her earning an income by giving tuition. - No, it was all cash that was being put into the account. Can we still use her bank statements? Also, will she have to write a letter (NOC) that she wants her money to be counted for this application or only showing her bank statements along with their marriage certificate will work?
If her income is below taxable limit, you would want your dad to financially support your mom's visit. He must provide a Letter of Financial Support + his tax assessments + bank statements (that can pay for two persons). - Will this Letter of financial support needs to be a legal document or a simple written statement on white page with his sign will work?
Your parents would also include evidence of any other financial investments: FDs, RDs, mutual funds, shares/stocks, LIC, etc. That said, only liquid funds can be stated as 'Funds available for my visit'. - Sure.
How long their visas will be valid for will depend on the assessment made by the visa officer. There is no 10 years' default validity. - Ok
Does this amount match their income + their tax returns? Or was some of it transferred by you? - None of this is transferred by me. All this is their own amount. One more query - regarding to this - I have some amount in my Indian account. Can I transfer the same in their account? Will this cause any issue? Because the current 4-5L is their own amount, not even a single penny is mine. But now, If I want to transfer the amount from my Indian account to their account, then will it cause some problem to their case?
Also include property ownership documents + property tax receipts, etc + their employment documents + their tax returns, etc etc - Sure
Do remember: All claims must be supported by evidence - Sure