Of course the expansion of space is being considered by astronomers. In fact, it's pretty much the only thing they are considering. The redshift due to expansion of space is the way that astronomers know that it came from 13.14 billion years ago. What you do is look at the lightwaves very carefully. They will be stretched out (which looks like redshifting) due to the expansion of the universe. The longer they have been flying along, the more stretched out/redshifted they will be. The group cited in the article measured a redshift (a measure of this stretching) of 9.4, which is the largest we've ever observed; we conclude that this light has been traveling longer than any other light we've observed from a single source (the cosmic background radiation is way more redshifted).
A number of very clever methods allow us to identify just how long the light must have been traveling for it to received a particular amounts of redshift. This is an application of the relation known as Hubble's Law. If you use it, you find that light with a redshift of 9.4 has been traveling for about 13.14 billion years.
This method is used so routinely that you'll hear cosmologists talk about time in terms of redshift, like "Ionization occurred at redshift 17" rather than "Ionization occured 13.5 billion years ago" (those numbers are made up).
We know that some galaxies are moving away from us faster than the speed of light and we know it by measuring the redshift, but how's that possible?
The following papers give good explanations:
http://users.etown.edu/s/stuckeym/AJP1992a.pdf
http://arxiv.org/pdf/astro-ph/0011070v2.pdf
In summary, Hubble Law: $v = H(t)D$, where $v$ is recession velocity, $D$ is distance, and $H(t)$ is the Hubble "constant" at a given time, requires that beyond a certain distance velocity is greater than the speed of light. If recession velocity at the location of a traveling photon were greater than the speed of light the entire time the photon from a distance galaxy were traveling, we would never observe the photon. A photon emitted from a galaxy moving away from us faster than light, initially is also receding from us. However, the photon may eventually get to a region of spacetime where recession from us is $<c$. In this case, the photon can reach us. The exact relationship between red shift and velocity depends upon the cosmological model, but according to the above references, galaxies with red shifts greater than ~3 were and are receding from us faster than light.
If they're moving away say at 2c, how would the light of the galaxy? even reach us?
Only if the photons from the galaxy reach a region of spacetime where recession velocity is $<c$.
How do we measure "redshift" for something faster than light?
Red-shift is measured as the change in wavelength of the light, but rather than interpreting the results using special relativity (which would result in $v<c$ for all red shifts), the results are interpreted in the context of a cosmological model and general relativity.
Best Answer
As long as the universe is decelerating, light emitted from sources beyond the Hubble sphere will eventually reach us. See this post for a detailed answer: If the expansion of the universe slowed what would we observe?