Do all seedlings look the same?

No, but they are very similar.

Do you get more than one seedling per seed?

only 1 plant per seed. I have dissected a Meiwa seed to see many embryos but only 2 time did I get more than one seedling per Meiwa seed. I will dissect my next NZL seed.

Is New Zealand Lemonade believed to be a hybrid of Meyer and a Mandarin? If so, then it's a complex hybrid and who knows if it will be true to type. Could be or not. Have you done searches online to see?

That is why I ask. I was not able to find the answer by using Dr. Google.

 How many varieties of Meyer lemons are there because some people say they are sweet others say they are bitter so there must be several varieties this only make sense

Howard, this discussion is on the hybrid ‘New Zealand Lemonade’ and not on Meyer

 Remember the Meyer lemon  is also a hybrid   logically different trees of the same hybrid wi have different taste

This discussion is not about taste.

  I was using some common sense   of what I said  on various Meyer lemon trees the fruit is sweeter than others  then technically how can there be only one variety  doesn't make no logical sence

 Hybrids Will  vary in flavor and become polyembroinc

Meyer is a hybrid and it is not polyembryonic. You will not likely get a Meyer if you plant a Meyer seed. On the other hand, Citrandarin, also a hybrid, most often grows true-to-type from seed. So you never know unless you experiment.

Someone who owns a NZL could dissect the seed.