In American English, "There are two of us here" is the grammatically correct one. HOWEVER, the expression "there are" has virtually disappeared from the American lexicon. One rarely hears it, whether referring to singular or plural. "There's" has taken over and, since, one hears it everywhere, Americans assume (apparently) that it's grammatically correct.

Actually... both can be said, and both are grammatically correct. "There are" is obvious, so I will not say anything about it. As for "there is two of us here"... it is grammatically correct, rather than giving a profound explanation I will just say that it is like saying: How many people is it? It is only John and I... The fact that there are two people doesn't make the sentence wrong. It is taken as a group... pretty much like the explanation provided by Padraig. It certainly doesn't have anything to do with being lazy as Eliot may want to think... I hope this helps... Mario

"There are two of us here." = correct "There's two of us here." = wrong, BUT...everyone says it because we're kind of lazy.

"There are two of us here" - because it's more than one, it can't be 'is'.

There are two of us here. "are" is used for plurals and "two" is plural. There is a pair of us here. "is" is used as there is only one "pair".