Hello and welcome to the boards!
It's always wonderful to see someone get a hamster. My only advice is to keep an eye on them and supervise your sisters with the hamsters. As far as handling goes, every type of hamster is a little different, but all of them will get used to you as long as you take your time with them, spend time around them, and make sure they get used to your scent. When it comes to younger children, it's best that if they are under the age of 12 (some say
that they simply observe from a distance and learn the basics and try not to handle them much. It's easy for a child to get distracted or scared at first. My son is 4 and my daughter is 8, but both of them still get overexcited around my hamsters, so I don't let them mess with them other than looking at them through the cage.
I am aware of your last statement, it's just best to make sure to put this information out there anyways. If you want the Djungarian go for it! I don't see why there would be a problem at all with having one of those. Also, since kids to tend to catch colds more often from being at school and around other children, to make sure that if either of them gets sick to keep them away from the hamsters at all costs as the hamster(s) can catch the cold and it's much more detrimental to them than us humans.
Good luck on your selection, and honestly go with what your gut tells you! It'll be a great learning experience for both of your sisters on how to keep the cages clean, how feeding works, etc; my kids help in cleaning and changing the water out and sometimes they'll give my hamsters a treat!
Again, welcome to the forums!