Chamber music is music specifically composed to be played by a small number of musicians in a private room or other small venue.
While compositions written as chamber music are often performed in large concert halls, the number of musicians remains small.
The string quartet (two violins, a viola, and a cello) is one of the most popular chamber configurations.
Yes, a full orchestra would be a grand gesture, but I do think chamber music is more suited to an at-home wedding.