Okay, there are is merely right or wrong and a 50/50 chance of each so it’s basically the equivalent of tossing four coins in the hopes to get one or more of htem to turn up Heads.
There are 16 possible outcomes of which only two have them all in agreement and only one of them results in none of them knowing the answer (which is also one of the two situations where all of them will agree.) so the odds of them having at least one person with the correct answer under those conditions is pretty good: 15/16 or ~94%.
However, because of how groups work, it will generally take at least 2 people having the correct answer to convince the others. There are 6 possible ways that two people will have the correct answer, and 5 more that either 3 or all 4 will.
In other words, there is a 5/16 (~31%) chance that a majority will be correct thus leading the group to give a correct response. a 6/16 (37.5%) chance of a squabble that could go either way, and a 5/16 (~31%) chance of them screwing the pooch.
Based on that, one would think that the odds are truly 50/50, but in reality the odds are that if 2 (and only 2) of them have the correct answer, the other two will have different wrong answers or that one or both will just not know, leading to a 2–1-1 vote or at least one abstention and thus the group will be more likely to give a correct response.