Future consequences: if they try to renew their visas, will they be denied because I didn't go back? Will the Consul find out what I did?
Depends on your country of residence but that is entirely possible. Visa applications often require the demonstration of "family ties" that would compel visitors to go back home. Having a close relative who stays illegally in the US will certainly not help.
Will the Consul find out what I did?
Probably. You will get flagged as an illegal immigrant as soon as your tourist Visa expires. US immigration may discuss this with your embassy, but that depends on the country and the relationship.
- Is there a way I can legally stay in the US for a job for more than the 6 months I'm allowed on my tourist visa?
No. In order to find a job you need a legal authorization to work in the US. See https://travel.state.gov/content/visas/en/employment.html. There are various types of visa but they are all hard to get.
Final thought: DON'T DO THIS. It is illegal, you will be deported if you get caught and you will not be able to enter the US again for a long long time, or never.