Their age could be the fault, though the skunk scaring them could have caused some lingering harm or inspired onset of their premature decrepitude. Given their type, at this age they can generally be counted on to show rapid and premature ageing due to the sheer scale of overproduction they have been bred to supply. It's very, very hard on them, and it's why they don't last long.
Production reds and other high production layers are generally ready to cull after 2 years old because that's how they're bred to be, burned out at a young age. The commercial layer diets almost never contain enough nutrients for them to live long or attain full health because if they receive enough protein and oils and fats they either go into moult, or take a seasonal break from laying like normal hens, or go broody. Keeping them deficient is how one gets every last possible bit of high production out of them before they die. The diets they are generally kept on are formulated specifically to wring that out of them, and it is at the expense of their health, so naturally their eggs are inferior as a result, as far as nutrition goes.
The diseases of malnutrition are many and often take a very long time to show but are pretty hard to fix once an animal has not only been deficient all its life, but been pushed into overproduction and bred from parents who experienced the same for many generations. It's not a coincidence that many chooks are hatching with established deficiency diseases now.
Anyway, this is not intended to harp on at you at all, but I do believe they are a false economy for most situations. I have kept such hens myself and never will again. I much prefer mongrels who eat far less, lay almost the same, then continue to lay years after their poor-quality, high-consumption, disease-prone equivalent has rotted into the soil. Since I keep them for health reasons I wouldn't surrender extra quality eggs for a few more poorer quality eggs per year.
There are a few things you could do to try to get them going again, though.
If they've never moulted in their lives, or only once so far, then they could be going into moult now. If so, letting them off their diet so to speak and giving them greater protein etc now, and letting them moult, will eventually likely see them laying again, but generally you can expect fewer eggs, less often, and quite possibly some will never lay again.
If they have never taken laying breaks before, of at least a month, they are well and truly overdue. Like us their bodies need time to rest, replace old cells etc but when compelled to produce heavily and nonstop they don't have that luxury. Reproduction takes a lot out of a female, even if she doesn't complain in ways we understand, and even if the eggs are infertile.
Because their overproduction prevents normal health maintenance they will take even longer to restore themselves than normal hens who take at least one break a year from laying. Giving them a really good diet while they recoup can speed things up, possibly.
The oyster shell can be too hard to serve as anything other than grit, which is of course necessary, but judging from the signs, your hens are suffering from probably both premature ageing from overuse as per the average for such hens, (not your fault), and lack of calcium, the latter being the part that you can address. A serious scare also takes certain nutrients out of the body to some extent and prevents others being utilized for a while. They would likely benefit from an easily digestible source of calcium-magnesium right now, even crushed eggshells would help a lot.
But the bottom line would be that now is probably the time to get fresh hens. You can probably not expect regular production from these anymore, it may happen but the cutoff at 2 years old is often quite drastic. Some will keep laying longer but sporadically, but generally if you want regular and reliable eggs you would probably do well to invest in a new few layers, younger ones. I keep differently aged teams for laying, mothers and daughters, so when the mothers go into brood or moult or whatever, the daughters have hit POL and are laying, and when the daughters need to go into brood or moult the mothers are back into laying, and this way I get eggs through winter as well when others with their same-age teams are going without.
Best wishes.
