I understand what you're saying about the birds not being in direct physical contact. However, you still don't have any sort of biologically secure situation that disinfecting toys between the two birds would be of much significance.
Some diseases and mode of transmission:
Polyoma - contaminated droppings, crop excretions, feather dust (air), and respiratory secretions
Psittacosis/Chlamydia - droppings, inhalation
Clostridium - ingestion, wound contamination, inhalation of spores
Newcastles - ingestion or inhalation of particles
PBFD - thought to be spread by feather dander, fecal matter and other secretions from infected birds
You'd have to have your birds in a different dedicated air supplies, bathe and change your clothes in between handling the two birds, have shoe baths or shoes dedicated for use only with each bird, etc. So, contaminated toys aren't really that big of a concern if you're not going to practice true biosecurity procedures.
Technically, buying anything from a store that has birds in it is a risk to your birds when you bring the item home, including food. Going anywhere there are birds you risk bringing home disease to your own birds on your shoes and clothes. Taking your birds outside risks disease from inhalation of disease causing agents.
I have basically five "sectors" of separation at my place so if I do have a disease outbreak, I can reasonably implement quarantine procedures. I have 5 acres. My conures are on one corner of the property, I have a second set of birds on the other end of the property, I have a third set of birds out the backdoor, I have a fourth set out in between the house and the garage, and the fifth set are the birds in the house. Should there be a disease outbreak, I can reasonably treat the area where there's disease in a quarantine situation as it's in completely separate airspace - I would need to feed and service them last, shower and change my clothes before going near the birds not in quarantine.
Despite my five sectors not being in direct contact, I do risk unknowingly transmitting diseases at this time to all sectors, prior to disease detection/outbreak, because I don't change my clothes in between servicing each sector or otherwise practicing biosecurity procedures. For the most part I'm usually not even washing my hands in between servicing each sector.
Goes back to you can't keep them in a bubble. Sorry if that was TMI.