Dear Sheeberi, I faced the same thing when I visited our doctor with my 15 months babygirl. Moreover, she asked me if baby was already able to join 2-3 words and make short sentences....At that time and up to now, the only thing my daughter says is some animal sounds what she learnt from children'songs and cartoons like boo-boo, muuh,baa-baa.... but though she doesn't speak, she understands what I say and with verbal communication can explain to me what she wants. I speak to her Russian, and my husband speak to her mother tounge uzbek and plus all cartoons and songs on TV are in english and me myself try to speak to her english from time to time, like stand up, close the door, come here, sit down and etc. And she understands. And when she goes to kindergarden she will learn czech as we live in Prague. This was the biggest challenge for me, when i was afraid to put too much on my baby's shoulders at such an eary age. But this realy works, she grabs what we say, little by little, step by step she gets there. And that is definitely true, that those babies who start speaking later than others, will speak whole words and make sentences easily. once they speak, everybody will understand them. Plus multilingualism is also an issue here. I didn't speak until 3, and then I was easily understood by russian and uzbek speakers. That is why i am not that much worried about late speaking, what I am worried about is how else should I introduce english and czech to her, with the help of flash cards, how do i divide the input of those languages. So be patient and you will be very surprised when your twins start speaking! I wish you lots of energy and joyful moments in this uneasy task-waiting for them to speak :-)))
Good luck!