Hi and welcome to Purrs- enjoy it but be warned it can be rather addictive!
What I would say to one of my adopters (I'm in charge of homing with Cats protection) is that it's better to get the single cat or pair that know each other settled first before introducing another. With kittens though, they are rather more adaptable so there is a strong possibility they could cope with a new home and meeting a new compnaion at the same time if things are handled carefully. I definitely wouldn't separate the two that know each other so you need to decide whether or not you have the space to do the introductions, whether you are used to cats enough to go from none to three all in one fell swoop and whether or not you have the time to devote to training and bonding with three kittens. I know I found having just one very demanding but as a person who has 4 cats, I can honestly say I couldn't imagine having less than 3 again.
I would talk to the rescue they are coming from about what they advise as they may or may not be happy for you to home all three at once. If they are reputable they should also give you lots of information on kitten care and how to go about introducing the three kittens to one another. Ensure that the kittens are healthy and vaccinated when you adopt them as well as being regularly wormed and de-flea'd. Do do your research before comitting to adopting them as it's important not to get any nasty shocks.
In terms of the practicalities- to start with they could probably use the same carrier if large enough but as soon as they grow (which is very quickly) you will need three separate carriers. In terms of litter trays, I stand by Vicky Hall's (feline behaviourist) magic rule of 'one tray per cat plus one more' and so have 5 trays for 4 cats but they will definitely need at least one each for the rest of their lives and cats are rarely happy to share trays- again, do you have space for this?
If you discuss thoroughly, seek advice and decide you are ready for three cats to have everything they need, then I think it's great that three cats have a lovely, forever home. Just remember that they will be adult cats in a matter of months and what happens when they are growing up from kittens to cats can have such an important part to play in what they are like when they grow up.
Good luck and enjoy your new feline family members.
Also, remmeber itr's in the rules that you must post pics when they arrive- however many you have!
