Golly, that is a big egg!
Though that doesn't mean that it is fertile.
There is only one way to know if it's fertile - incubating them.
If you have an incubator, continue to incubate the eggs, whilst turning them at least 3 times a day - Then at around day 7 or 10, candle the eggs or do the float test on them. If there's a chick inside, it means it's fertile, if not, then you can eat it. (Unless you have a broody hen to incubate the eggs )
For the float test, if the egg floats and bobbles around, it's fertile, if it sinks, it's not (I think that's how it works ^-^)
Otherwise, if you've seen the male mount at least one of your females and you know for sure that that's her egg, then there's a high chance it's fertile.
It could be a double-yolk, which might be fertile but is more likely to have problems that will result in chick death before hatching.
Or maybe you'll be really lucky and get a chimera chick, where the two embryos will fuse into a single individual! Bilateral chimerism is a rare form found only in birds. You could hypothetically get a bird that is two different colors or even half male/half female right down the middle of the face!
If it is fertile, it would probably need help getting out of the egg. There's too much room in that shell for a full-term chick to be able to get enough leverage to pip through the shell properly.
Exciting prospects, though!