Is it legal to charge different property management fees to the owners of the same building?

There should be a specific basis for charging. You can refer to the management entrustment contract. You are not the first to charge different fees, but in the same format, the same floor, the same management service requirements, and the same conditions, it is generally the same. If the reason is reasonable and both parties agree, then there is no problem.

If there is any objection, it can be negotiated through the industry Committee.

I'll tell you again that every owner's rights are the same. No matter you are an institution or an ordinary resident, the owners' rights and obligations are the same.