I know you cannot apply more than 2 referrals per membership renewal, but will you get emails notifying you about the 3rd+ referrals?
From what I know, the email is generated to let you know that you have earned a $25 discount on your next renewal. So, I would imagine you should not receive a third email within a membership period where you have already received two referral bonuses.
Either way, the thing to remember is you can only get a maximum benefit of $50 per renewal.
H-Man is correct. You'll only receive them when you get the discount.