The advice offered by previous posters has been excellent. They know what they’re talking about.
Other problems you will find with outdoor cats. First, the very real possibility that each time you let them out to roam might very well be the last time you see them. It’s a dangerous world out there, with cars, dogs, other cats, cruel people, and all kinds of other dangers (I wrote this before I saw CrazyCatLady’s reply, which is much more comprehensive on that point). Second, outdoor cats are much more likely to bring home parasites and diseases, which not only shorten their lifespan, but can also be passed on to the other pets and sometimes even the family. Third, if you think stepping on hairballs in the middle of the night is disgusting, you’ll really love climbing into bed with dead birds and half-eaten rodents that kitty decided to leave as a present.
Also note that indoor cats will be extremely curious about the outside world, and may become escape artists. If you wish kitty to stay happy, healthy, and indoors, keep a spray bottle on the doorstep and fire a couple of shots inside as you slowly ease the door open.
As to the question of should you get cats, just keep these thoughts in mind.
First, cats are destructive. If not properly housetrained / tended to, they will shred your furniture, tear curtains right off the wall, destroy your carpets, knock precious knickknacks to the floor, and pee and poop in all kinds of unexpected places. This does not even begin to describe the damage they might do to you from time to time. If you are not an extremely patient person, or you have expensive furnishings, pass on, friend. Get a goldfish.
Secondly, taking good care of any pet is expensive. The food and litter add up quickly, especially if you get the good stuff. Cats need regular shots and periodic checkups at the vet clinic. Emergency medical treatment is quite costly, and most vets will make you pay upfront. If you have a medium or long-haired cat, periodic professional grooming may prove necessary. Maintenance on a single healthy cat (not counting property damage) may average around $20 per month, but can shoot up to $300 or more if there are any significant health problems.
Third, there’s a lot of work involved. Litter boxes must be cleaned frequently (every day if you can manage it), because cats will turn up their noses at dirty litter boxes and relieve themselves on your bed, in your shoes, or in a pile of clean laundry – this is known as “leaving you a memo.” Claws should be trimmed periodically, which is a two-person job if the kitty decides he/she doesn’t enjoy the ritual. You will be cleaning up cat hair from every exposed surface, even if kitty gets a regular brushing. There are perfectly good reasons why those experienced with cats nod sagely when they hear the saying “dogs have owners, but cats have staff.”
If all of these dire warnings still haven’t put you off, then maybe having cats is right up your alley. And getting two kittens from the same litter is a wise choice (provided that they’re properly weaned). They won’t have to “get used to” one another, and will be more likely to get along well and keep one another entertained. Plus you should be able to feed them both the same food, which will save you from some major inconveniences.
Good luck!