Speech Question

Baby Bouchard

My son will be 18 months old tomorrow, we have been overwhelmed with physical therapy for both him and my daughter that I hadn't really paid too much attention to his speech delays until recently. We had a speech evaluation and while he's not terribly off the charts, he is delayed, we start therapy Wednesday. His speech is very monotone and rough, he doesn't have any words for eating/drinking/etc, the only words he does say are Momma/Dadda (he didn't say those till 16m), however he can repeat short song lyrics! He says "let it go" "up above" (from Twinkle Twinkle), "Pat, Pat, Vroom" (from Little Einsteins), etc...yet can't say cup or eat or anything like that. Any ideas? He and his sister are being evaulated by neurology and genetics, they both have facial myopathies, hypotonia, lax joints, etc.