Each of those girls should have a dark past.
One of the girls was promised to some other man by her parents. She escaped, and the parents are now doing everything in their power to get her back. Even if it means killing her friends. She is generally the good natured, high spirited girl, shy, and good with household things. Typically moe. However, she is actually inhabited by a powerful ancient spirit, which she can summon if she gets agitated enough, and those who she loves are in mortal danger.
The second one could be an actual princess, heir to the throne of a dictatorial, genocidal regime. She left her country, because she did not want to have anything to do with them anymore. To leave the country, she used secret technology, which she now possesses, including an experimental teleporter and highly advanced weapons.
Her former family is now pouring all its resources into getting her, and especially the stolen tech back.
This girl has a princessy attitude, tsundere, and she is good with organisational matters, finances, and above all, technology and science. An inventor, too.
The third one would be a former child assassin, highly skilled and lethal, who left her profession to begin a new life. She is now hunted by contract killers sent by the victims’ families and the organisation she once worked for.
She has a hard and rough outside and manner, a typical kuu-dere, silent and laid back.
She is excellent when it comes to the handling of all sorts of weapons, hand to hand combat, athletics and stealth, setting deadly traps, mixing poisons, etc.
Now the three are constantly assaulted by their enemies, and they must work together to repell the attackers with deadly force, to end their plight permanentlym and to find and rescue their foster father.