This is personal choice.
We have adopted two at the same time many of times .
However we recommend that you take one at a time and 3 months later ideally , unless you have extra time to focus on socialisation for each kitten,.
This is because kittens can bond together rather than with humans, they already have security with litter mates already and less need for humans.
A short gap of 3 months is perfect and more than enough time for human bonding .
Our kittens are so highly socialised i wouldn’t be concerned, nor do i find this a issue with our kittens, and we are more than happy to adopt 2 at a time .