My DD is 3 also and we're teaching her two languages, as well. She seems to understand everything DH says to her now, but we watch movies in the second language and she can almost never tell me what a character just said, or even what is going on (minus what is visually obvious). Were not sure if she just isnt paying attention to US, or she really has no clue whats being said.
Its WAY harder than we imagined it would be. I try to reinforce DH's lessons, but I just dont know a lot. So, I can only ask her to translate back and forth. Which she does with some reluctance. However, if he says something to her, she will yell to me, "Daddy says..." So, we know shes understanding. Speaking is like pulling teeth.
I keep reminding him to refuse to respond to enlgish. Or to immediately translate her response and ask her to repeat it. Sometimes she rolls her eyes, but if she is asking for something, she MUST say it in DH's language or she wont get it. It seems harsh, but I believe its the only way. He forgets a lot though and even though he remembers to only speak in his language, he forgets to force her response in his language.
We have another baby due at the end of the year too. So, now I'm just telling her, you have to make sure you practice, how else will your baby brother or sister learn if you can teach them? And that is definitely a good motivator.
Best of luck! Bilingual is a fabulous gift to give your kids! But its a ton of work on your part!!!
Oh, we are also considering putting her into classes with other children whose main language is her second. Where the whole class is taught in it. If she see's lots of other children speak that way, she will follow! It is such a sweet thing though to see DH and her going back and forth in their own secret conversation (its taken 3 years though and she pretty much answers in yes, okay or no). Its a very sweet bond and helps make him feel even more at home to hear his native language in the house.
I think it will be great for your DD's bond with DP!