Unfortunately, it is not surprising why all three applicants were refused.Yes,my younger brother who has completed his study in india.
This is how your applications would appear to the visa officer:
Yourself:
Entrepreneur (but not demonstrated adequate business ties) + first visit to a visa-required country (Thailand won't count as travel history) + no strong ties to return to (no property ownership, no dependent family members, etc) + no compelling reason to visit
Your dad:
Retired (no employment ties) + first visit to a visa-required country + no strong ties to return to (no dependent family members, etc) + no compelling reason to visit
Your mom:
Employed (but not sure how long it is before she retires) + first visit to a visa-required country + no strong ties to return to (no property ownership, no dependent family members, etc) + no compelling reason to visit
To have some chances of a TRV approval, it would be best if you apply alone, without your parents. In this situation too, you would need to demonstrate that your business ties are solid to return to