The genre is Fantasy. All I request is some new, creative ideas to spice it up a bit. If you know any nice, fancy words those help too.

The main character is a princess named Millie (short for Millivere) who isn't all that proper. She has 6 sibblings. She and the four younger ones were captured by some villains...
I'm stuck.

Giant magical adventure to get them back while also bringing down the entire empire of the villains. Maybe she gains the trust of a great horde of people who are in fear of the villains also.

Brilliant!!

Or how about, that as she and the young ones are captured and millie is sent over to another villain where he has a crush on her her and teaches her good manner, grace, tactfuness, caring and femine, while the young ones escape and trie to rescue her from her admirer who tries to seduce her:)... now that's love and excitement for you.

I like it.

It sounds like a lot of room for romance and comedy too.

She has 6 sibblings. She and the four younger ones were captured by some villains...
You have mentioned five children. What about the sixth one? Could he or she turn out to be the hero in the adventure?

Then let an enchanted wizard get in and inform the child about his or her own destiny and help them find the right path to free their country and their family.