I agree that they all look troublesome. The 1/2c should be gray, the 1c ink and paper don't look right, and the 1/4c color is a green, but not the right green.
The quick test is the pearls, or marbles, around the frames. Yours all have too many. Yours have horse and other detail issues, too.
The best site I know for this issue is here:
http://www.mystamps.net/venezuela/i...cudos02.htmlHe has nice pictures of genuine stamps, and then identifies 12 forgeries.