Its interesting about the modelling behaviours from siblings- I ahve a little boy in my class who has a severely autistic older brother (virtually non verbal- goes to a special school) and for the 1st few weeks of school (kindergarten) he modelled those behaviours eg, refusing to speak, hiding under a desk, wouldn't do any colouring/cutting etc. I left him alone a bit then gently starting helping him or doing things with him and he is fine now but it was very difficult at first.

DS is going really well at speech, he is starting to self correct and he can say "L" now!!! He has become obsessed with a PS3 game and we have to monitor how much he plays it or he loses the plot when we turn it off