gravekeeper's descendent

during tourney today, i got 2 desendents on my field. I wanted to destroy opponent monster by activating one effect and tributing another. Some say cannot and some say can. Maybe having 2 descendents on the field is a rare case but is it possible to do so?

English version of the effect:
You can Tribute 1 face-up "Gravekeeper's" monster you control, except this card, to destroy 1 card your opponent controls.

If that does not answer your question well enough, in simple words, yes you can sacrifice the other.

thanks