But we have had to accommodate lots of them in units that don't allow pets.So if there's a chance you might have an animal in there anyway, you might as well have some say in it and get compensated.

It sounds to me like your parents' landlord has been extremely accommodating over the years, much more so than most would be if an existing tenant moved in extra people and a pet without prior permission.  

I'm sorry, I can't accommodate you, but I understand that you might not want to continue living here.  

We have several student accommodations and the prime lease-up windows are late February - April (for those who are very organised and looking for a lease starting in May or September) and June - July (for those who are less organised, or were accepted in to a programme last minute).

I always acted as fast as I could to accommodate them but if they are in cahoots with the AC company I don't know what I can do ....of course they are using it as an excuse not to pay rent. 

You must allow an emotional support animal as a reasonable accommodation for your tenant, but you don't have to allow a non-tenant's emotional support dog on your property.Here is a document that explains the laws for CA regarding the differenty types of support animals, and whether they have the right to go anywhere in public, etc.

Being required to provide a reasonable accommodation is not the same thing.

You've made reasonable accommodations and should not be liable for their hotel expenses.  

He rents houses to them for their overflow students who can't be accommodated in their own properties.

Working with tenants to accommodate their needs is customer service.