Define exactly what you need each to do. Think it thru, are they range guns, CCW daily, just nice to have? The firearm fits a purpose to it or you could just buy the cheapest and be done - or the most expensive, too.
You need to ask yourself what the range and target for each will be. That's what a firearm does, extend your reach, and it makes holes in targets. In one respect it's pretty limited in getting it done, it only makes a hole in something, albeit with a lot of force.
So it applies force downrange. How far and into what? A precision target pistol or deer gun?
One pistol might be for CCW, in 9mm accepting the theory it's the smallest working round available, with 6 shot magazine because personal confrontations are usually less than three shots fired. Single action with safety because that shooter has carpal tunnel and a long heavy trigger pull isn't working for him any more. Small, light, easily concealed - where another might carry a duty sized weapon in a larger caliber under a suit coat because it's issued and that's what he or she gets.
A target pistol isn't a CCW pistol. Same for rifles - they change, sometimes radically, all due to how far and at what you shoot.
The first thing you find out with the information is the cartridge that fits - not the cartridge that is currently the cool Bullet of the Month. Cartridges have this thing called "Ballistic application," which is jargon for how far it shoots and how much energy it still has left along the way. You pick the cartridge that is optimal - best suited - for the range and target you chose. It ranges from .22LR to .308 or even larger in pistols - if you can accept the idea of a 10" barreled AR10 with no stock. They sell them.
It also goes to being careful what gun in that specific cartridge might be on the market, because they DO make things simply because they sell, not because we need them. In don't expect I will ever CC an AR15 pistol in 5.56 despite the legality of doing it in my state. The circumstances would be extremely rare in my lifestyle. But - a compact 9mm, sure, got one just for that job.
That's how you figure out what guns you might buy. What range, what targets? It's exactly the same thing the military means when they say Mission Drives Equipment. Soldiers don't go on missions with the wrong kinds of guns. Shipboarding teams go with 10.5" barreled SBR's, not 20" M16's. It's crowded inside a ship with narrow passageways, you need firepower but range is limited. Pistols don't carry enough ammo in the circumstances.
Once you have range and target, the caliber falls in place, that means optimum barrel lengths, what kind of action, what optics, then furniture. In that order. Not exactly what many shooters do, because more often they see something that looks cool and then work back from that regardless of whether it actually fits their needs. And far too many just jump on a Brand bandwagon to wave the flag and be part of the tribe - as if that defines their character.
What are the guns for?