One quick suggestion would be to fill an empty pop can with little pebbles or stones. Every time the chihuahuas yelp shake the can hard and yell no. Eventually they will learn that when they yelp they will get a un-pleasing result.
Get a spray bottle and fill it with water. Whenever the chihuahuas yelp, spray them in the face with the water. Just a light mist spray will be effective, the chihuahuas will not like this and they will stop yelping.