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The recent demonstration of the growth of two-dimensional (2D) antimony-arsenic alloys provides an additional degree of freedom to tailor the basic properties of the emerging group-V 2D materials. With this perspective, herein, we propose and conduct a comprehensive first-principles investigation on this 2D group-V antimony arsenide (2D As x Sb y), in both free-standing form as well as on the common substrates of Ge(111), Si(111), bilayer graphene, and bilayer hexagonal boron nitride (h-BN). Structural and electronic properties of the 2D As x Sb y are evaluated for different compositions, different types of atomic arrangements for each composition, and different lattice matched interfacial configurations of the composite heterostructures for the four substrates. These systematic studies provide property benchmarks for this new class of group-V 2D materials. This analysis reveals microscopic origins of the interfacial interactions, orbital hybridization, charge transfer, and the resulting electronic structures of the 2D alloy. We predict that a change in the frontier states leads to an indirect-direct bandgap transition according to atomic arrangements in the monolayer As x Sb y. On substrates, the relatively strong interfacial interaction between Ge or Si with As x Sb y suppresses the semiconducting properties exhibited in free layers, while the weak van der Waals interaction between graphene or h-BN with As x Sb y preserves the bands of the alloy. We conclude that 2D group-V alloys As x Sb y give a large material phase-space with very interesting electronic properties. [ABSTRACT FROM AUTHOR]