I am very sorry to hear that you are unhappy with your veneers. It is unfortunate that you did not have the opportunity to view the veneers before they were bonded. In our office we do a diagnostic waxup, make the temporaries to mimick the permanent veneers, and give our patient ample time to approve their veneers before bonding. With the strong bonding cements today, the veneers can be removed, but only by drilling them off. If your teeth were not prepped, you can remove them and polish the teeth. However, if your teeth were prepped, you will have to have new veneers fabricated that meet your expectations.
Without doing an exam or seeing xrays, it is hard to recommoned exactly what you need, but maybe I can give you some guidance. If a tooth has no fillings or a root canal, and especially in the front, I would recommend only veneers. Veeners are a good choice if you are unhappy with the appearance of your teeth and have tried teeth whitening already. However, on the posterior teeth, which it sounds like you have root canals and crowns, I would recommend crowns. Also, there are different types of crowns. Usually, we prefer non-metal crowns in our practice. It is important to be able to have a discussion with your dentist about all of your options.
I would recommend a nightguard first. Does the veneer seem to loosen in the morning? Many of us grind at night which puts tremendous forces on our teeth. It is important that veneers be bonded properly and even though it is a very strong bond, grinding can loosen it. A nightguard would prevent the forces that can loosen the bonding. I know this can be frustrating, but a nightguard will also protect your other teeth as well.
It sounds like you are a good candidate for braces. Braces are a great solution for correcting crowding, spaces, and large overbites. There are many types of braces too, such as conventional metal, tooth colored, braces on the back of teeth, and clear braces. Ask your dentist for a consult so you can find out what is best for you.
Veneers should not be placed over loose teeth. It is not healthy for a tooth to be loose. It could mean that you have periodontal disease and bone loss. With proper periodontal treatment, however, your teeth could tightned up, and then you very well may be a candidate for veneers.