I am not opposed to butchering the roosters, but it seems daunting. Shooting a bird is one thing (less up close and personal) but using an axe or slitting the throat is another. I don't know if I could bring myself to do it. Any suggestions to make it easier?
I use killing cones with a large single-action PVC cutter. It's gruesome, that's unavoidable whichever method you choose, but to me it's the fastest, most humane, and most error-free method I could find. You can't miss the mark or do it incorrectly. Just hold the bird's beak in one hand, slip the cutters around the bird's neck with the other hand, and squeeze hard and fast. And it's over just like that.
Lots of folks swear by the "broomstick method". I haven't tried that, so I don't know. It's bloodless, and they say death is certain and quick, so it's one I would consider.
The only other thing I can think of to make it easier than these, is to have someone else do it. You could also take them to a local meat processing facility, where people take their cows, pigs and deer to be processed. Most of them will slaughter chickens too. And they'll butcher and package them for you as well. You'll have to call well ahead of time (months, even) to reserve a date.
I also have a question about the age to butcher, my birds always grow really slow and only reach a decent size at around 6-8 months. Is this normal or am I doing something wrong?
It's normal for the Orpington breed. There are other breeds that grow out faster, so they're more economical with the cost of feed. However, most sources agree that the best age to slaughter chickens is around 16-17 weeks, before they are sexually mature. At that age, the meat is still tender. Once hormones are involved, it gets tougher and stringier. With your Orpingtons, you could probably hold off a couple of weeks longer.
"Decent size" like those you find in the grocery store are from a specific breed called CornishX or Cornish-Cross, which grow out to butcher size within 8-10 weeks. Backyard flocks of Heritage breeds typically don't reach that size by 16 weeks, unless you're growing meat-only breeds.
More on that below.
They are being fed on layer pellets, would grower pellets help considerably? I don't want them to grow so fast they suffer as a result, but I assume that's more about breed than feed.
Growing chickens that are not yet laying, and roosters, should NOT be eating layer feed. It has far too much calcium and can cause organ failure, particularly liver and kidneys. There are better options for a mixed flock, like an "all-flock" feed, chick starter, or game-bird type feeds. And then you offer a dish of oyster shell on the side for the added calcium - your hens will eat the oyster shell as needed, chicks and roosters will ignore it. They know what they're doing.
One last thing, I've always heard that homegrown chickens are for the soup pot only. Is this true?
Not true at all, *IF* you slaughter them before sexual maturity. OLDER birds are for the soup pot only, as their meat has become tough and stringy. I tried frying one once, and couldn't even bite into it. Like shoe leather. Had to throw it away, such a waste. I got myself educated. Now, I always slaughter my cockerels at 16-17 weeks, they're decent size (to me), then I brine them for 3-4 days for extra tenderizing before packing and freezing. Always tender, juicy, flavorful whether fried, baked, grilled or roasted. The flavor IS slightly different than commercially-grown chickens. It's more, well, flavorful and has a little bit more body to the bite - I think that's due partly to genetics, but also because we don't keep chickens crowded into small cages who never see the light of day and muscles are never exercised.
Chicken meat from the store can be used in so many ways, is this even possible with chickens butchered yourself (duel-purpose specifically)?
See my answer above. My breeds (mixed) are all dual-purpose: Rhode Island Reds (RIR), Barred Plymouth Rock (BPR), Black Australorps (a type of Orpington), Easter Eggers (EE), and a few others from rescues. I butcher and cook them all. Fried, baked, grilled, roasted, barbequed, smoked, breast tenders, buffalo wings, chicken salad, chicken and noodles, chicken strips or nuggets, gizzards and livers (yum!), enchiladas, whatever! Delicious.