The 1095-A is in my wife's name and includes the 3 of us as covered individuals for the full year. Since the PTC was based on our much higher income, allocating 100% of the 1095-A to our non-dependent son causes him to have a massive tax refund of 14k+ (while our tax remains unchanged). He barely made enough to cover the premiums so doing this seems like it would cause problems with IRS.
Yes, this is legal. You may make allocations with people on your plan that file a separate return in any way that you choose. The only stipulation is that the allocations sum to 100% and you are in agreement.
Here is some information you may find helpful: I'm on my parents' 1095-A form. What do I do on my return?