Yes, but slowly.
Fantail goldfish are a hardy breed, strong swimmers and they compete well for food with the ryukin, shubunkin, comet or common goldfish; making these goldfish breeds good tank mates for your fantail goldfish.
Perhaps you mean 'Clamped fin'. Clamped fin is caused either by parasites or poor water quality. If you mean 'Fantail'. A fantail is a fish with 2 tails instead of one. They are harder to keep than goldfish but are much prettier
yes
Yes, lobsters regrow legs, claws and antennae, but can not regrow their tails.
Female Fantail goldfish can not get pregnant they lay/scatter eggs when they are chased by males . So you have nothing to worry about.
no
Goldfish are peacefull fish and do not normally fight with one another.
it has a short tail
A fantail goldfish can be any of the goldfish colours which can include any or all of the following white, gold, silver, copper, blue, orange etc etc.
Survival of the fittest
My friend had the same problem. Her dad thinks (and we think) that the tails on the fantail are small and colorful, and so they look like goldfish food. Hope this helps!
They are both goldfish and so can breed with one another if they are of different sexes.