Nothing illegal about contacting the tenants, regardless of whether or not you're the legal owner. However, entering into agreements with the tenants may be difficult if you are not the legal owner yet.
I don't know of any law that would be violated by your contacting the existing tenants.
However, I can easily imagine situations where your contacting the tenants - especially if you do not become the owner - could subject you to liability for interfering with the existing owner's contractual relationships with those tenants.
This information does not constitute legal advice and does not establish an attorney-client relationship.
As pointed out in responses above that even though not "illegal" yet potential liability issues as well as inability of contractual creation and as pointed out in responses to your similar posting you have an agent and all communications and inquiries should be funneled through them to avoid potential issues of liability. Best of luck.
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My colleagues have all pointed out issues that you need to consider before contacting any of the tenants. Best of luck.
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