Oh my, his poor world has changed and now the added stress of grandma being mad at him.

If you have done all the treatments for possible physical problems, than I too would say it is stress related over grooming. And of course, with all that grooming, hairballs (and vomiting) is to be expected.

Was Tama bonded with one of the 2 kitties that are no longer with you?
Does your mom have any animals that Tama might not like?

Among your treatments for anxiety, have you tried stronger medicine than herbals?

Do you think you could confine him to your own room? Maybe he needs to "start over" getting used to a new place just a little at a time?

I am so sorry this is happening to you both. Maybe someone else has more practical experience with this problem.