We can provide some further information on the sketch:
a. The original drawing was done by Gaspard Duche' de Vaney, but was lost. A watercolor from this orginal is attributed to either Tomas de Suria or Jose Cardero. Most cite Cardero.
b. If you require a high resolution copy of the drawing and an academic source I believe that it is available at the Bancroft Library, University of California Berkeley (the Robert B. Honeyman Jr. Collection).
c. The mission in question was San Carlos Borromeo de Carmelo, the second mission in the chain of missions established by the Spanish in the territory they called Alta California. The mission was founded on June 3, 1770 and initially located at the presidio in Monterey (which became the headquarters of both Alta and Baja Califonria). In 1771 the mission was relocated a few miles south in the Carmel Valley.
d. The principal Indian linguistic group in the Monterey area were Costanoan, primary the Mutsun tribelet. For details see Costanoan by Richard Levy in Handbook of North American Indians, Volume 8 (California), pp. 486-495.
e. The princpal padre was the (second) Father President of the mission chain, Fr. Fermin Lasuen. I do not have information on the other Europeans.
A day after we answered this question we received the following email:
Thank you very much for your very prompt and most helpful reply to my inquiry