Violin - Can double stops be played when the strings are not next to each other?

Absolutely, but it's harder on a modern instrument. As RedLitYogi says, the convex bridge (not the fingerboard!) affects your ability to play more than two adjacent strings. A tight bow means you can only normally hit two notes at once.

1. What are double stops on a violin?
2. Which of the following instruments can play double stops?

What are double stops on a violin?

In music, a double stop is the technique of playing two notes simultaneously on a stringed instrument such as a violin, a viola, a cello, or a double bass.

Which of the following instruments can play double stops?

They help produce variety in color, texture, harmony, and counterpoint. Double stops on the violin, viola, cello, and double bass occur when two strings are played at the same time.