About pronunciation of 大家
This phenomenon is called 懒音. And it can be very common in casual spoken language and it's really a personal habit varies for different people. In the case of 大家, the consonant of 家 is omitted for an easier pronunciation, since the vowel of 大 and 家 are both open vowel /a/, and /ʨ/ in the center is somewhat hard to articulate. Therefore, it becomes something like /ta a/.