Multilingual? Multiliteral? Both?

First topic; language.

We are basically a bilingual family; my wife is a native Mainer, or what the Mainers say "Mai-nah." And I am Japanese. It has been always a challenge to teach kids more than 2 languages. Depending on environment they were in, they might speak more than 2 languages fluently, or they might understand  but will speak only one language fluently.
How about our kids? My 5-year-old boy and 2 1/2-year-old girl understand English and Japanese perfectly, while both verbalize English more than Japanese. My wife also speaks to them in as much Japanese as she can. And my boy seems to recognize some of Japanese alphabets.
I tend to hope my kids to speak, listen, write and read both languages just like I can...but here are some key things for multilingual education.
1) The words "bilingual" and "multilingual" actually mean "to be able to speak and listen to more than 2 languages."
2) Being bilingual or multilingual does not necessarily mean "being biliteral" or "multiliteral."
3) There have been evidences that people can be multilingual but not multiliteral, and vice versa, and both.

In our case, at this point, our goal is multilingual. Literacy will come later...let's see.