They are normal goldfish, how big is "massive"?
Do they look broadly speaking like this?
Maybe with longer fins, but with that single tail and a straight body?
These are your 'normal' goldfish. They should grow to be at least a foot long (12", 30cm) and may grow longer. Some have been known to reach two foot (24", 60cm). They can live for 15-25 years, with 30-40 being a ripe old age but not unheard of. These goldfish require a very large tank that will allow them plenty of swimming room and that will house 1-2 heavy external filters. If you want to keep these guys in a tank, it will need to be at
least 6 foot long and if they grow to more than 12", they'll need an even bigger tank. In short -
these are pond fish.
Fancy varieties are a little easier to keep, requiring slightly warmer water (15-24C) and without such heavy space needs in most cases. I would be reluctant to keep a single fancy in less than 30 gallons (3-4 foot tank) and I would allow at least 10-15 gallons for each additional fish. Fancies can still reach 12" but this is a realistic maximum size. Most stick between 6" and 10". Some people recommend 20 gallons for a fancy goldfish but if you ever see a 8" fancy goldfish in a 20 gallon tank, you'll know it needs more space.
Yes, this information is very different to what you hear from pet shops and what you might be used to from your childhood. The sheer amount of lies, misinformation and misconceptions that abound about goldfish are the reason they are probably the most abused pet in the world. Many live for only a few months in aquariums due to the lies spread about using goldfish bowls and small tanks.
Goldfish are a major committment and IMO, it should be illegal to give any animal away as a fairground prize. 99% of those fish will die well before their time due to poor conditions, and not through any intentional cruelty. You are one of the few that will actually consider researching this 'cheap', 'easy', 'throw-away' pet and I'm just sorry that you now find yourself with 5 fish that you'll either need to rehome to a pond or that you will need to spend a considerable sum to accommodate. Poor you and poor fish.