What is true in the relation of difference is true about other relations. The nature of any term, unless that term is itself a relation, is attributes or properties in the non-technical sense. The nature of an apple means its roundness, redness, juiciness, and so on. So a change in any properties would be a change in the apple's nature.
Now a relation is not a property. But when a term has a relation to anything else, it also has a property because of that relation, a relational property, and that property belongs to its nature just as much as any other property.
If Ann is the mother of Beth, then you are asserting the relational property of being the mother of Beth. And this property is not itself a relation in the sense in which the relation of motherhood is. Hence, even though a relation is not a property, it gives rise to a property. And these properties are a part of the nature of what has those properties. The properties of being 'above the beast of the field', 'a little lower than the angels', and 'the mother of Beth', belong to Ann as part of her nature.
But the relations could not be diffferent without the properties being different. And the properties could not be different without their terms being different. For the properties are part of the terms. Therefore, if all relations were different, their terms would also be different. Consequently, all relations are internal.