Hello, and welcome to the Community!
I'm not sure that you've provided enough information for anyone to properly or responsibly answer this question. There are A LOT OF VARIABLES that come in to play when it comes to being able to "house" any two or more birds together of any species.
First of all, when you say "house" together, do you mean keep them in the same cage, or do you just mean having them living together in your home, but not in the same cage? Because it's possible, obviously, to keep multiple birds of different species in your home as pets as long as you can separate them, not only into different cages, but sometimes they have to be in different rooms...If you're talking about whether or not you can put 2 or more birds together into the same cage, this is a question that is impossible to answer, as it DEPENDS ON THE 2 BIRDS YOU ARE WANTING TO PUT INTO THE SAME CAGE...In-general, you should ALWAYS ASSUME that you will need to keep each bird in it's own cage, especially if you're talking about housing two different species of birds together, as one may be larger than the other, which can be dangerous...But regardless of size or species, there is absolutely NO GUARANTEE that any two birds with get along or even like each other, even if we're talking about two birds of the same species, such as two Budgies...
-What species of "parakeet" are you talking about? There are many, many different species of "parakeets", from the smallest, the American/Australian Budgie, to the much larger species, such as the Moustache Parakeet, or the Alexandrine Parakeet. Obviously you cannot house a Moustache Parakeet with an American Budgie...typically.
****Any time that you put two birds together, meaning simply in-contact with each other (I'm not talking about putting them in the same cage), there are a few different outcomes that can happen:
-They may bond very closely to each other and be fine being housed together after a period of time (YOU CAN NEVER JUST PUT TWO BIRDS INTO THE SAME CAGE ON DAY ONE, NOT EVER!!! ALWAYS HAVE AN INDIVIDUAL CAGE FOR EACH BIRD YOU BRING HOME!!!!)...If they are the same species of bird and of the opposite sex, these pairings usually end-up mating/breeding.
-They may seemingly like each other and play together, but not bond closely with each other (they have there moments of nipping and such, and cannot be housed together in the same cage). These birds can be out together for playtime, but only under-supervision.
-They may not like each other much at all, but simply tolerate each other (again, they will have their moments, usually some are violent/aggressive, and cannot be housed together in the same cage obviously). These birds can sometimes be allowed out together ONLY under-supervision, but usually they do not want to be out together for play-time, and usually you have to have separate out-of-cage-times for each bird by themselves.
-They may absolutely hate each other and be violent and aggressive with each other every time they see each other. Obviously they cannot be housed together in the same cage, but these birds also cannot be out of their cages together at all, not even under supervision, as they constantly try to get-at each other.
So as you can see, this is a very hard question to answer for you, as the answer is TOTALLY DEPENDENT ON THE 2 SPECIFIC, INDIVIDUAL BIRDS YOU ARE SPEAKING OF.
****So while we can tell you that it is possible to house 2 "parakeets" of the same species together in the same cage, for example 2 American or English Budgies, or 2 Alexandrines, or 2 Moustache Parakeets, it is all going to depend on the type of relationship that 2 specific, individual birds have with each other...NEVER GO AND BUY 2 BIRDS AND 1 CAGE, OR IF YOU ALREADY HAVE A BIRD AT HOME DO NOT EVER BRING HOME ANOTHER BIRD WITHOUT BUYING A CAGE FOR IT TO HAVE AS IT'S OWN!!!! You can never, ever, ever, just assume that it will be okay and bring a new bird home and throw it in the same cage as your current bird on the first day you have the new bird...or the first week or month for that matter. It takes time to see what kind of relationship or bond that your current bird is going to have with any new bird you bring home, REGARDLESS OF WHETHER THEY ARE THE SAME SPECIES, SIZE, ETC. OR NOT!
***Also, you have to remember that if you already have a bird, it has been living in it's cage since you brought it home, and THAT IS IT'S CAGE, IT'S "SAFE PLACE", IT'S PROPERTY!!! Even the most friendly birds are usually very territorial about their cages, toys, stands, etc. So it's not unusual for even 2 birds who eventually bond with each other or at least get along with each other during out-of-cage-time, to BECOME VERY AGGRESSIVE AND EVEN VIOLENT when the other bird goes near it's cage...