Not your husband's problem. The photography studio needs to contact either the landlord or the mgmt. company (which ever one leased to them) and THEY are the ones to either provide better insulated walls or some type of sound barrier, or let the studio out of their lease.
The studio should have been told by the mgmt company about the sound level prior to renting - so yes, they should have know what they were getting into.
Your husband has every right to run his business w/ the existing schedule. He should not change his schedule to accommodate the studio. The disruption in schedule can cause a loss of clients and business!!
Your husband seems to be trying to help to resolve this issue the best he can - but it's not his job or responsibility to do so.
He needs to tell the studio that they should contact the mgmt. company or landlord w/ any complaints or demands that they have. Your husband has NO LEGAL obligation to rearrange his schedules, or to insulate the building for the studio. Of course he should still be civil, but he should definatley be firm about having the studio contact the mgmt. co. from now on.
To be on the safe side, have your husband check the lease that he signed to see what his responsibilities are.
Good luck - we have have rental homes and it's amazing the unreasonable demands some tenants make.