Sorry to hear of your loss. Having done alot of research on Mareks specifically from my information it can and dose stay within the areas exposed for months or longer even. Any birds you handled with it then handled others have already been exposed. It is common and treatment once symptoms start can not be helped. Vaccines do little if anything for the other strains. So even if a bird has been vaccinated they can still carry the virus. Some carry it without any real issues others may be effected more. Some may show symptoms later in life. That all said you have the hens already and they have at minimum been exposed via handling and there is no test or way of knowing while they are alive unfortunately. Many birds have and carry it without knowing. So I personally would not rehome and possibly expose someone else's flock. Just keep caring for them and handle what comes or doesn't. This certainly is not the only trial that will arise raising them. Having dealt with this and many other issues over years this is how I would handle it. I have 3 coops with varying breeds and ages as well as rescues and mixed flock. The loss is always difficult.
I'm sorry for your loss.
Yes. I would keep them all and introduce them after the younger ones have been able to build their immunity. When your younger girls are beyond 5 months they should have a much better chance. There are different forms of Mareks and rate of death for each form. Many things can and may arise during raising any animals. The more of them you have the more loss you will seem to encounter. As with all pets (all of mine are) there will be loss unfortunately. It may be very helpful to get a book to have handy for reading in advance to know what to look for as I mentioned previously. There are signs when they start feeling not themselves and you can intervene in a timely manner for some things if you are aware. The Chicken Health Handbook has 2 editions and good information. Best wishes
