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@sharpcougar wrote:

The recipients on 1095 were the married couple

MIL did not receive a 1095A. 

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It sounds like the mom is a dependent of the couple.  Is that right?  The rest of my comment assumes that the couple is eligible to claim mom as a dependent.

If the couple claims the in-law as a dependent, it goes on the couple's return.

If the couple chooses not claim her as a dependent (so nobody 'claims' her) , the 1095-A goes on on the tax return which had intended to claim her.  The fact the couple CAN claim her, the couple signed her up for insurance, and the couple set it up so the 1095-A is in their name STRONGLY indicates the intention was to claim the mom.  So it goes on the couple's tax return.