I'm not sure that this will work because Teams will need oauth authentication working which will require a hybrid environment between the O365 tenant and on-prem Exchange. Since their syncing with their local AD and not your environment, it won't have access to your Microsoft Exchange.
Now, in September 2020 Microsoft released an update to the Hybrid Configuration wizard ( https://support.microsoft.com/en-us/topic/september-2020-update-to-exchange-hybrid-configuration-wizard-54278b2b-ea62-31e4-8be6-3b16dfa1b9b3) that allows you to do multiple configurations between a multi-tenant Exchange and multiple O365 tenants. This will require you to do the Azure AD Sync with your environment though which will involve you having a sync server per tenant that you want working.
Essentially, I don't think it will work with the way you have it setup but if you plan on keeping them on your Exchange you could change their syncing over to you and setup the hybrid config to make it work (we are in the process of testing and playing with this configuration but not done)