This amazing video shows an annular eclipse of the Sun by Phobos as seen from Curiousity. This one shows an eclipse by Deimos. My question is do these things ever both happen at once? Do you ever get simultaneous eclipses by Phobos and Deimos from anywhere on Mars?
About Mars moons, eclipses and transits (from NASA - Curiosity Captured Two Solar Eclipses on Mars:
Phobos doesn't completely cover the Sun, so it would be considered an annular eclipse. Because Deimos is so small compared to the disk of the Sun, scientists would say it's transiting the Sun.
Phobos does pass in front of Deimos but the current models of their orbits still have an error margin. From the same page:
There's still a margin of uncertainty in the orbits of both Martian moons, but that shrinks with every eclipse that's viewed from the Red Planet's surface.
That means that as of right now, your question does not have a definitive answer.
And here both Phobos and Deimos transit the Sun at the same time
This is the link for Celestia 1.6.x:
A couple of images from the result: