Strange behaviour in the blue tit nest

This year, i decided to set up a camera in one of the nest boxes in my garden (unfortunately, last year the blue tits did not have a successful breeding season and none of the chicks were able to fledge from the nest). The female laid 8/9 eggs and they all hatched last Wednesday. I have been watching the nest daily and i noticed this morning that 4/5 of the chicks had disappeared from the nest overnight. In addition, the female is spending long amounts of time on the nest and the male is not bringing in food consistently, i.e: sometimes it is bringing in lots of food but there are also long breaks between nest visits. Furthermore, the male is bringing in large insects/ caterpillars, which are not suitable for the chicks. The male will place the insect in the mouth of a chick, the chick will struggle with the large insect and the male will remove it from the mouth of the chick, only to consume it himself. i am not sure how much of the food is actually being consumed by the chicks and i am wondering if the male has another nest nearby, which would explain its absence from the nest at certain times during the day. Is there anything that i can do to help the remaining chicks, such as supplying mealworms in the garden?