First after Felipe becomes Felipe VI Cristina will not be in the royal family anymore nor Elena. as they will be be sisters of the king not daughters. of course they will keep their titles and salary. But no inmunity as Cristina has now.
The law of old stated an older boy will be become king, but Juan Carlos was sure to change it so that a woman could be. Now Felipe VI will have a son no problems.He has two daughters the law was change for that in mind. just like in UK.