They will definitely not have frozen 4 in a straw so I would suggest thawing the best 2 first and see if both survive, if not thaw the next straw, maybe 50% will survive. FWIW, I would transfer 3 if 3 survived but definitely not 4. If 2 survive out of the first straw, just transfer the 2 though don't go onto thawing the next 2. I transferred 4 terrible 3 day embies with my first successful cycle and started with triplets, on my last cycle I transferred 3 blasts as one was very poor quality and they wouldn't freeze it. I got twins and I am sure one is the bad embie as one always measured a day behind which is what the embryologist said when we spoke before transfer. Good luck with your cycle.