Telescope is almost a misnomer here. It will be “looking” at other satellites, not astronomically distant objects.

The influence of gravitational waves will be seen in changes in the relative distance to each of the six satellites.

Yes, but also no.

Each side of the triangular array will measure nearly 1.6 million miles, or 2.5 million kilometers.

The satellites themselves may be small, but the interferometer antenna they’ll collectively form will be huge.