In both, the 'formal' answer is to use 'it'. 'Either' means 'one or the other of two things'. Strictly speaking, it is grammatically singular. In formal texts, it is best to use singular verbs (e.g. is, has, was, etc) with 'either':
Either of these is the perfect car for Mary.
Does either of them come in blue?
Check whether either of them is here.
Has either of them visited?
Does either of you know the answer?
In informal contexts, you may find both singular and plural verbs:
Check whether either of them has/have gone.
Does/do either of you know the way to San Jose?
In either-or constructions, the 'proximity rule' says that the verb used should agree with the part closest to it.
Either the accused person or the police officers are lying.
Either the police officers or the accused person is lying.
That rule is not observed everywhere, and some writers may follow another - that the verb should be singular if both items are singular, and plural if at least one item is plural:
Either shortbread or cake is available.
Either chocolates or cake are available.