I'll start with the issue in your latter three questions. I would say that a female and male would successfully spawn provided of course the male accepts here as his mate (I'll return to this later). I am not especially well versed on Apistogramma taxonomy, but I may be able to explain a little bit. I always think the background helps us to understand the fish and many like me find it interesting.
Apistogramma is a large genus and there is ongoing discussion among ichthyologists that it might be more than one genus. There are four lineages and a sublineage (the agassizzi sublineage is sometimes considered as a distinct fifth lineage) recognized by most sources, following Koslowski (2002), Stawikowski (2005) and Miller & Schliewen (2005); the latter used preliminary phylogenetic analysis (DNA) so the fact that the findings support the two prior studies is very relevant. Within these lineages there are groups (one has one group, two/three have three, one has five) and then each of these groups contains one or more species complexes [plural of complex, which some consider more correctly to be complices but I find complexes more frequent in scientific work in the hobby]. Each complex contains several species.
The agassizzi sublineage comes within the trifasciata group, and contains four species groups. One of these is the agassizzi, which contains the pulchra complex as well as the agassizzi complex. There are several species. This complex has a very wide distribution through Amazonia, and the geographical separation has resulted in several natural varieties that more extensive phylogenetic analysis may one day confirm as distinct species. The point from this is that they are very closely related, about as closely related as two or more distinct organisms can be phylogenetically, so there is no reason to suspect they cannot inter-breed.
If that hasn't completely made you give up...now to the male/female. The best way to discern this is to observe the fish in the store tank for some time. I have stood in front of dwarf cichlid tanks for 15-30 minutes, motionless (so the fish hopefully tend to forget my presence), looking for obvious (again hopefully) bonding pairs. The males will push and shove somewhat, but basically ignore the females, or at least any female they "accept" as a possible mate. Females tend to be a dull shade of grey to brown to dusky yellow unless they are in breeding mode.
Acquiring a female for your male(s) is a bit difficult. First, if you retain the two males, more than one female is advisable. One of the traits of this complex is their strong polygamy. So a harem (one male, 2+ females) works well. There has to be sufficient space in the tank obviously, so the females do not get in each other's way particularly when guarding eggs/fry. Second, the fish need to accept each other, but I readily admit that I do not know just how strong this trait may be in this species. In rams it is absolutely essential, but I have had Apistogramma species acquired as "pairs" that spawned.