you sure its not just veins?
i keep all my eggs in the incubator until the hatch day, then if they don't hatch i leave them there for 3 days after....
i don't take any eggs out in case i do mistake an egg to be 'dead'
also, maybe if it is a blood ring, one embryo could still ok, so leave it there! the other baby as it grows will just absorb the extra yolk.
hope this helps!~
good luck with your twins!
~Bantambury