The blood spot has absolutely nothing to do with the egg being fertilized or not.
I'm not entirely sure, but I thought there was absolutely no way to tell a fertilized egg from a non-fertilized egg? Once you collect your eggs (twice a day) and they head into the fridge, the point is irrelevant since that stops all growth and makes the embryo unviable.
I keep one rooster with my layers (~50 Speckled Sussex, Barred Rocks, Black Sex Links and Cornish). His name is Ollie. I keep my 6 other roosters away from the hens, using portable electric netting. Otherwise, all those roosters just chase the hens all day, and they don't eat and lay as they should.
One thing is for sure, the cockrels mature sooner than the hens start laying eggs. They will be harassing the hens for weeks on end, trying to figure out which end the vent is on, and it's just chaos.
I choose to keep the one rooster with them for lots of reasons. The largest is the hens like him. They follow him around like he's some rock star. It's typical to see 6 or 8 hens just following him like a posse. He also regulates any fighting the hens do. I call him the little feathered sherrif.
I think keeping one roo with your six hens should be fine. If he starts injuring them, then you need to deal with the rooster. You can send him to auction, eat him, separate him or sell him.