You could probably keep the silver aro's in a 240 indefenetly. Depending on the gar specie, perhaps ther could stay too, some get real huge, you need to identify what kind you have. Parrots should be fine. I'd ditch the tiger shovel nose before they get real big. YOu can not keep them permietly in a 240, they will out grow it. I wouldn't wait untill they are huge to try to find them a new home. It is common that you can not give away large fish for free because no one else has a tank big enought either. Most local shops won't take them (i own an aquarium shop) because they know how hard it will be to sell and how expensive it will be to feed and maintain them. For get donating them to the local zoo, the zoo gets call all the time wanting to take oversize animals off the owners hands. Get a really big aquarium or consider doing some thinning down. A 240 may seem like a big aquarium but you will quickly realise that it isn't. Hate to be a bummer but this is years of experiance talking to you....
Joel