All frozen foods should always be thawed out in the fridge. You can refreeze meat that you cook, you are not supposed to thaw uncooked meat and then refreeze the same uncooked meat.
I haven't heard of lentils/beans being hard to digest until 8 months, I know with dd we gave them to her in month 7. The latest info out there by some doctors is that solids should be held off until 6 months (not 4) and that you can start with a protein. With this said, I still didn't feel comfortable starting with a protein, I still have it in my head that their systems can't handle "longer to digest" foods, like proteins, until they get used to the easy stuff first.
I have frozen beans whole in the past. I made chili once and had too many cans of beans open as I wanted a variety of beans so I froze them and used them later in another batch of chili.