If the user requires to oay something even indirectly or not directly related towards on buying the property it still voids the matter being a donation. The client still needs to pay something in order to get that piece of ownership. There is really no donation happening at all. If you decide to continue this method and I hope you don't you would just be breaking a lot of laws and your clients would also be part of it. Just don't bury them into this kind of mess.
Okay, but if go this way:
Users will buy tokenized assets of "company", not shares of properties. (from Juridical person)
Then users can choose: they want to trade and transfer or staking.
In staking mode their tokenized assets will be frozen for 30 days, the system will choose "free" shares of properties and will give it by Gift Deed according to staking amount. (from Natural person).
So, basically they will "invest" in Juridical person, but getting properties from Natural person.
And since donor can stipulate conditions in a Gift Deed, conditions can be for example - "staking" and if they will decide to stop staking, it will just give me the ability to revoke Gift Deed.