I don't like to nitpick people's arguments for little slip-ups and typos, but the nationalities of the people in this movie are so integral to the plot it makes me question your entire understanding of the movie.
I think the Son came on the trip hoping to get close to a father whose approval has eluded him his entire life, and his 'getting in on the take' is partly revenge for that mistreatment and emotional damage, and an attempt to win the respect of his father.
The grenade (not landmine) was close to Otis, and also it was an old military reflex.
I agree they should have spent more time on character development for the bloods even though I think Otis got some good character time.