Is it possible for 2 religions to both be true? 
perhaps as long as they do not contradict one anouther at all.
I would say that is more possible for two religions to agree, than for two differing adherents to come to terms, but you used the word “true”, thus requiring my answer to be more exacting. I will use truth as in the correspondence theory of truth since the question itself necessarily tests the coherence (at least of each religion in respect to each other). That said, i think it more likely that (given that God exists) the different religions are all aspects of the same thing than that any one of them corresponds to the reality of the cosmos. And in this sense, they agree, albeit only in essentials. Religions are created by man to define God, certainly a futile task.
well if the basic tenet of Christianity is that there is only one God, and a basic tenet of Hinduism is that there are multiple Gods, how can they both be true?
Lady Sphinx,
before replying to this, I would like to know which religions could this be.
It merely depends on the combination.
what do you mean by ‘true’?
For two religions to be true in the sense of, absolutly right, well they cant be. UNLESS they are NATIVE or Less complex religions for more of a naieve populations.
The roman version of greek gods and the greek gods could be true. because they are one of the few with same gods.
True- As in, it is possible for both religions, for example Christianity and Judiasm, for both of their teachings to be true, without being logically contradictory.
Just for “purposes”, is it possible for both Christianity and Islam to be true?
The whole question centers around how anal you want to be about your particular religion. For instance when Jesus says in John, “I am the way the truth and the life. No one comes to the Father except through me.” You can interpret that a number of different ways:
(1) You can say, anyone who does not repent of their sins and belive that Jesus was God, and that gay sex is evil and unnatural, etc, etc, will go to Hell.
(2) You can say, it’s all a metaphor for some fundamental experience at the heart of every religion–that Jesus is taking himself to represent all faiths. “Through me” can mean through any spiritual experience.
(3) You can choose not to believe everything your preacher tells you to read.
(4) You can realize that the historical Jesus probably never said any such thing and probably wasn’t a religious exclusivist to begin with; so there’s really no real problem reconciling Christianity with every other faith.