It’s easier if it happens since birth, still
it’s okay to start later

The key is, if you aren’t on the run to go
live to Portugal or Greece (erm, I
wouldn’t recommend either at this “financial” moment ) so don’t need to
rush on their learning just let them ***listen*** to it

Don’t feel like you have to teach them as
if you’re a teacher, just pass on with your legacy and language as a part of it.
You may always use Portuguese/Greek as “code-words”, some families have
code-words that are invented. Each one of you may speak to them in each one’s “second
language” when not all together, don’t let them be confused, the family’s language
is English.

Give me your address and I’ll send you some
books (& music!) (ask for the same from Greek family), even if they don’t
follow your reading they will acknowledge the printed words, that will be nice
for the language programming too. I wouldn’t advice to try teaching them to
write second language before grade 4 once they won’t be using it.

Remember, if they listen to more than one
language, additional than family legacy, it “muscles” their language areas

I’m a preschool teacher and what I’m hearing/reading from my studies of language development and my work with speech-language pathologists in supporting children in my classes, is that it is most important to give your child a good foundation in his/her first language (in this case English, as it’s what they hear at home and in daily life).  If they are learning vocabulary/articulation/conversations well and are speaking confidently in this language, they will be able to pick up the others.  (In a couple of years, probably.) 

(I would suggest that you keep letting them hear the sounds of your languages from time to time, i.e. songs, lullabies, stories now and then, as it becomes harder for them to pronounce and use those sounds otherwise.)  The way to learn both languages fluently from the start, really, is by full immersion–to have each parent speak to the children in his/her language ONLY, which is pretty difficult (especially if there are three languages involved).  Don’t give up on your goal, just give them a few more years to become confident language learners.

We’ve gone both ways on this as we speak English to each  other but make and effort to speech our second languages to the kids when talking to them.  It’s hard cause I sometimes throw some greek in and italian in the same sentences cause i can’t remember the italian word.  I know it’s messing with their minds. However we will be sending them to italian and greek school once they reach 6 years old. Just haven’t figured out how it will work – 6 months on language and 6 months the other…crossing bridges daily over here.