A woman used contraceptive pills, and her menses exceeded(15) days, is it permissible for her to fast?

The maximum of menstrual blood is(15) days, but if it exceeded that due to a medication, or the like, then it is Istihadah(bleeding outside the monthly period), and in this case she should perform Ghusl(ritual bath), pray, and fast. Moreover, she is obliged to make up for the missed fasting days which exceeded her regular menses.

Am I permitted to perform more than one prayer within single ablution?

You are permitted to pray as many as you could within one ablution and to recite Quran so long as your ablution isn't nullified.

Is wearing a cap permissible for boys, or girls?

In principle, anything is permissible as long as there is no Sharia evidence prohibiting it, thus wearing the cap by boys is permissible as long as it isn`t done in imitation of the disbelievers. Moreover, a Muslim woman should avoid all that which attracts the attention of men because whatever leads to the forbidden is forbidden

A woman died at the age of ninety. Her living children are nine: two sons and two daughters. The youngest of her grandchildren, from her son who passed away one year before her, is aged thirty-two. Are these grandchildren entitled to the obligatory bequest although they are aged thirty-two and above?