I'm really sorry to see that he is so debilitated and it certainly looks and sounds like it could be Marek's. His crop is going to struggle to empty with his head down like that, so
@Wyorp Rock 's advice to prop him up and massage it is very wise. Another sling like you made for the other chick might be helpful for him too. If he still isn't earing with help after a couple of days, I would euthanize as his quality of life is obviously pretty poor. Since this is your second bird with symptoms, a necropsy would be wise. Some labs will euthanize them for you if you are able to deliver them.... obviously ask before you go. Most labs have a website with a price list, so do check that out. Marek's testing would usually be extra and there is a huge variation in testing fees from state to state and some state facilities insist that specimens are submitted through a vet, which usually incurs additional fees. Hopefully your state is not one of those. Some states even offer the service free whilst others charge a significant fee, so it is a bit of a lottery. If you cannot afford the service, there is the option to open him up yourself and take a look inside. A few of us are becoming reasonably experienced at this and if you can take photos, we can often pinpoint and discuss abnormalities and come up with an idea of what the problem was. Obviously this is not conclusive but can give you a good indication of the problem. For instance, visceral tumours at this age would strongly indicate Marek's but only PCR testing by a lab would confirm it.
I know how heart breaking it is to deal with this. It is 4.5 years since it showed up in my flock and it has been a hard learning process but there have been some happy moments when birds have made some pretty miraculous recoveries from outbreaks of it. They still have the disease and are prone to further outbreaks later in life but can enjoy a relatively normal existence in between. Once they lose interest in food, I use that as the red line to euthanize but in your boy's case it may be that his twisted neck is preventing food passing through his system rather than him actually having gone off his food. Unfortunately handling him n this condition will be stressful for him (imagine if you woke up one day and your head was like that and you couldn't control it or figure out which way was up) and you would be best to wrap him snuggly in an old towel so that he is unable to flap and stress himself further. It is my belief from my experience that Marek's paralysis does not cause pain but it does cause fear and panic and frustration and these things all add stress to the bird and make the condition worse, so keeping them as comfortable and secure and stress free as possible is important.
Keep up with the vitamin E and Nutri Drench if you are able and only offer him moist food. Improvement will not happen overnight but if he continues to refuse food and water, then ending it for him is the kindest thing you can do for him.
