Help with seperation anxiety?? For a puppy?

My DIL has an 8 month old Havanese puppy. He whines and cries loud and long if he’s left with anyone but her or me. She has checked with trainers and google about what to do. The problem is that she works at home except Mondays when he comes to me. I said I’d ask if any flutherites have dealt with this. My son is fed up-he’s been in the same house all the time but doesn’t treat him like a baby as we, unfortunately, did.