Is david Keith related to brian Keith?

no

No they are both born from different parents. No relation at all.

This question is answered under: Are actors Brian Keith and David Keith related?

I don't remember what the original small tattoo was that he had on his left arm as a young man, but much later in life he had it covered up with a large colorful tattoo of the Virgin of Guadalupe.

Yes... They are Siblings :)