Let `q_(max)` be the max-charge supplied by the battery between `A` and `B` so that no capacitor gets spoiled.
For each capacitor
`q_(max) =CV_(0)=C(100)=100C`
For the combination `q_(max)=C_("equivalent")(V_(max))`
`100 C=(2)/(3)C(V_(max)) rArr V_(max) = 150 V`
Among `150 V`, potential difference across parallel combination is `150 V`, potential difference across parallel combination is `50 V` and the potential difference across the other capacitor is `100 V`.