Gabapentin comes in a liquid form. It is not very stable and has to be refrigerated. The pills for it are very large, and would be difficult for some people. It helps to put large oval tablets on the tongue, with the point facing back and then drink some water and throw the head back and swallow. Some people find using a straw helps with swallowing.

http://www.brucemedical.com/mepiswsy.html

The B12 is typically a sublingual type tablet. These can be chewed up and swallowed --take on an empty stomach.

Most vitamins can be ground up and mixed into apple sauce or pudding.
If you give me a list of the drugs and supplements he takes I can look that up for you... which are safe to alter.

Extended release forms of drugs cannot be ground up. There are a few that may be broken in half, but one has to be very sure before attempting that. Always ask your pharmacist about extended release drugs and safety issues. Your pamphlet you receive with them, usually spells that out. Some drugs with tiny time beads in them can be opened into applesauce and swallowed WITHOUT chewing. There are a few of this type on the market.

If your husband has GERD, and doesn't realize it, he may be refluxing and irritating the throat during sleep. This may increase the gag reflex.