As long as the size difference between the frogs is not too great, i.e., the larger one can't eat the smaller one's even if he tried, than I think you're ok to house them together. I don't know about AGTFs eating each other though, they may not be into that practice at all, but it's best to be on the safe side. If you think the older frog could fit the others in his mouth you should probably house them separately.
Did you buy these frogs together, all at once and from the same store? Were they housed together before you bought them?
All frogs go through an adjustment period when you first bring them home. If he doesn't eat for the first week or two, don't panic, this is normal. If he doesn't come around by the end o the third week you've had him I would start to be concerned. If you start seeing bones, that is an indication that it's time to take the little guy to a vet and see if they can get him to eat.
All frogs are different, so your others may be eating and seem perfectly healthy, but this does not mean they aren't going through an adjustment period. Just give them all some time to get used to their new home and surroundings, and they should come around.
Where did you buy them?
Also, it would help to see pictures of your enclosure and know the size in gallons or dimensions, what you're feeding them and how often, what substrate you have them on, if there are any live plants in the viv and what they're called, and the temperature and humidity you keep the frogs at. If we see any abnormalities in how you're keeping them this could help to prevent illness. Lots of beginners make first time mistakes and by the time they realize something's wrong it's too late and your frog is already sick. The best way to avoid your frog passing away is to avoid illness all together, so if you provide this information we can let you know if you're keeping them at ideal conditions.
Welcome to the forum, you'll find a lot of friendly and knowledgeable people here, and if you have questions don't be afraid to ask, someone will always be there to help you.