Say my friends and I(age 20) drink in the basement of my fathers house. Now let's suppose that one of my friends drives home drunk and gets in an accident. Is my father in anyway legally responsible?
As to whether your father would be criminally or civilly liable, the answer would vary depending on the jurisdiction you are in, and you have also not really provided enough facts to answer the question.
He would almost certainly be criminally liable if he provided alcohol to minors. In some states, he would also be civilly liable to your friend or persons injured by your friend if he provided alcohol to that friend. In any case, he could probably expect to be sued, which is never fun.
No he wouldn't be providing us with alcohol. He would just know what we were doing and not stopping us.
If he does not actually provide the alcohol, that changes the scenario slightly. However, in some jurisdictions, knowingly allowing minors to consume alcohol in your house might be sufficient to make you civilly liable for their injuries or the injuries of someone they hurt. Again, I do not know what the criminal law in your jurisdiction would prohibit.
Putting aside any moral implications, any way you look at it, it's generally a bad idea from a legal standpoint.
There will likely be a criminal statute in your jurisdiction somehow relating to "contributing to the delinquency of underaged persons" or something similar. Furnishing a place for the activity very well may fall into that category.
If he knows that underage people are drinking in his house, he'd be liable.
Liable yes, is anything going to happen? In Texas there are private property laws. And in Louisiana no one gives a fuck. Hope that helps