On what positive evidence do you deny Ra, Odin, and Zeus's existence? On what positive evidence do you deny the existence of leprechauns? If you don't have positive evidence against their existence then it is not reasonable for you to deny their existence. According to your flawed reasoning, EVERYTHING within the realm of imagination is to be considered plausible until positive evidence can be presented against it. Tell me, what evidence would convince you that fairies do not exist?
Theists, some theists that is, because not all theists are the same, get the world, or more precisely, reality - backward.
They, like paarsurrey here, want to what they believe in and for everyone else to accept their belief as real first...despite the lack of evidences for what they believe in.
This position is not at all logical. Because otherwise - like you have said - then everyone must accept other gods to be real, by default.
And like you have said, going by his logic (twisted as they are), we will have to accept fairies to be real. Or angels with 4, 6 or 8 wings, or angel with four faces (or 4 heads), etc. Or the ridiculous jinns, creatures of smokeless fire, shapeshifters in the Qur'an. Muslims might as well as believe in fairies, if they can believe in jinns.
Paarsurrey may say no one can disprove God, but can he disprove Ra, Zeus or Odin? If he can't, he has to accept them as real too.