Ellas estan amigas.
Ellas estan amigas.
They are friends.
5 Answers
Ellas son amigas es correcto! (At least it is correct if you are only referring to two or more girls/females!)
Ellos son amigos = They are friends (This refers to two or more males in a group or a mixed group of guys and girls!)
If you were to use Paralee's guidelines I believe that the verb Ser is used here because it is talking about characteristics. The verb ser is used here I know that with 100% certainty even if the reason I have given here might be wrong.
Another example is: Somos amigos para siempre = We are friends forever (by implication we will always be friends!)
I hope this helps 
Se habían hecho amigas.. They had become friends, just, as an add-on.
'Ser' and 'estar' are easy to confuse. "Ser" is used for "descriptions" like in your example and also "origin" (She is from Spain") and time. "Estar" is used for "locations" (She is here now), and "conditions" ( She is tired).
Ser is for descriptions, origins and time ( D.O.T.)
Estar is used for location and conditon (Lo. Co.)
Hope this helps.
This is a great question because it barely falls under one of the "ser" or "estar" so-called "Rules."
It's sort of like "Soy estudiante," which seems like it would take "estar" because I probably won't be a student forever...it's a short term condition. But rather, it's a description of what I am in the moment.
"Somos amigos" is a description of who we are to each other at this time, even though we might not always be friends.
This is a perfect example of why we can use the "temporary vs. permanent" rule for "ser vs. estar."
This is the best lesson on Ser vs. Estar that there is.
CORRECT!! Good job! Ser (soy, eres, es, somos, son) is permentant and Estar (estoy, estás, está, estamos, están)is temporary!
