Hi,
Your dogs will suffer no ill effects from the bones you give them as they are so infrequent. (Along with pancreatic problems a high fat diet will reduce your dogs ability to take up useful proteins.)
Bloat is the common name given to gastric dilation. This condition is very serious and requires veterinary attention FAST. It is often caused and complicated by gastric torsion. This is where the stomach has turned right over, sealing the openings to both ends.
Both conditions will need surgery and you must get your dog to a vet ASAP.
The gastric dilation is caused by excess gas and fermenting food in the stomach. Causes include a foreign body blocking the gut. Gastric torsion sometimes seems to happen with no cause but is usually seen when a dog has been vigorously excersised after feeding.
Symptoms begin a few minutes to several hours after feeding. A rapid bloating of the stomach is seen and the dog is restless. This quickly worsens to the point where the dog has trouble breathing and will be in extreme pain. The dog will become unconscious and the stomach will eventually rupture.
It is, however, normal to see some distension in the stomach after feeding. If this is worrying you try splitting the feed into two meals. Or measure the distension so that you will know if it abnormal.
These conditions are obvious as they cause such rapid bloating and such extreme pain.
To help avoid these don't excersise for half an hour before and an hour after feeding. If your dog is a wolfer of food try a raised food bowl and do not over feed in one large meal. Larger dogs are more prone but small older dogs are also presented.

This is pretty rare and is easily recognised so don't worry too much. If it does happen it is vital to telephone a vet, explain what is happening and be ready to take your dog to the surgery quickly. As I said, it is normal to see some distension and for occasional gas to make the stomach area feel a little hard sometimes.
If this emergency happens to your dog you will know!