Why think that a property couldn't be a person?
1. "Properties are abstract." But "abstract" and "concrete" are just terms of art. It may be that being abstract entails not being a person by definition, but then the question is whether properties are abstract in that technical sense.
2. "Properties are necessary beings." Let's grant first that properties are necessary beings. It follows, then, that no property can be a contingent person. But properties being necessary beings is still compatible with a property being God. Moreover, it is not clear that all properties are necessary beings. It may, for instance, be the case that there are haecceities, but they only exist when exemplified.
3. "Properties are multiply instantiable, but it is nonsense to speak of multiply instantiating a person." I actually don't see where the nonsense lies. If g is greenness, then g is multiply instantiated, i.e., several things stand related to him in the relation of instantiation. Suppose someone said that all green things stand related to me in the relation of instantiation. That would be false, but it would not be nonsense: the relation is just one that, as a matter of fact, the green things do not stand in to me. Moreover, not all properties are multiply instantiable. For instance, divinity is not (at least on one Trinitarian-compatible disambiguation of "multiply"). Nor are haecceities.
4. "Properties are causally inefficacious." But what is the justification for this? Properties are theoretical entities—they fulfill some theoretical roles for us, and we get an epistemic hold on them qua properties through their fulfillment of this theoretical role. So, for this objection to hold up, we'd need to show that the theoretical roles that properties fulfill are ones that require them to be causally inefficacious. But that seems clearly wrong. Maybe the theoretical roles that properties fulfill are ones that do not require them to be causally efficacious (Plato might disagree). But which of these roles requires them to inefficacious? Properties explain the grounds of predication. That does not require inefficaciousness. They explain the grounds of similarity. That does not require inefficaciousness. Maybe they explain individuation (Leibniz thought so). That does not require inefficaciousness. Each of the theoretical roles that properties fulfill requires them to have certain positive characteristics, such as the ability to be instantiated. It may be that sometimes the positive characteristics are incompatible with other positive characteristics. But I don't see how to make a case for that.