Any knows if there's a DNA difference between siblings (both males) to verify who the son belongs to? And what samples i should taking for the test...any doctors to comment?

Of course there is. You remind me of Daniel Jr. in Ugly Betty. Just google "paternity test shanghai"

http://www.genetree.com/ http://www.familytreedna.com/Default.aspx?c=1 http://www.genetrackhk.com/eng/index.php