Yes, they would learn faster if trained together because they'll see each other do the trick and get the treat. However, if you train them together there are going to be lots of noises and hypered kitites that would try to steal each other's treats.
So the first thing to teach them is going to have to be the rule "No worries, everyone is gonna get some". After they learn that you won't leave them without a treat, they'll allow each other take treats and would be more calm about it. So to how you do that, choose a praise word (or use the clicker) and after saying each kitten's name say the praise word or use the clicker and give the treat to the mentioned cat. Be aware that you'll have to be fast in this process (the first few seasons only), have lots of treats and not let a cat take the other's treat.
You can also train them with wet food on a spoon which I think is really good because after they learn to calm down at WET food they'll be calm at any other food sense wet food is really the BOMB. But I'm warning you it's harder with wet food as they of course will be super hyper to get it at first. I personally chose to start with wet food with my two kittens, which made them less hyper and crazy to get anything I try to give them.
Remember, for the first few seasons you're going to have to STUFF your kittens with whatever you train them. That is, unless they don't seem interested, if not then don't give them a huge amount because they'll lose appetite. That will teach them to be more calm about treats or wet food or any other food you give them. Say each cat's name loud and clear and then give the treat after either the praise word ( ''good'' or ''good boy'') or the clicker.
Of course because they are cats, it's better to have their names make a different vowel, such as Leo and Caddy. Why I say use a praise word is because the cats can learn by time that the one you're looking at while saying the praise word is the one doing the desired behaviour. And to answer your question, no you shouldn't use their names in every command, you want them to understand the command we as normal people speak. But you can use their names to draw attention and to make the cat understand it's her turn. Just remember while saying the cat's name keep all your attention on that cat not the other, even if the other performs a learnt behaviour which you taught some time before. After getting the cats used to their names everything gets easier for the trainer.
But keep in mind that you may need to take one cat in a room and train her without the other, when you do that use it's name a lot, she or he will associate their names better. It's not a must, it's just better to have each cat have private training time other than the training they have together.
If you want a certain cat to respond and the other do nothing I have but 4 things to make it all better:
- When you ask a cat to do something say it's name then ask the command, and when the other approaches ignore it intirely.
- Keep full attention on one cat.
- Get the cat used to it's name better by having private training time and don't forget to let her hear her name alot while training.
- Use the cat's name only when you want her to listen or look at you and make it in a clear voice, and give her either play or attention, or even treats or nice words every time, don't say her name and just look away or do something else.
I'd like to tell you to give her a treat everytime you call her name so she remembes it better but that's not necessary as you can call her name to play or to pet her. When you call her to come to you, that's when it must be a treat or dinner time everytime.