violent thoughts. short temper

Honestly hitting them in the head and threatening them is only going to make it worse. It sounds like your siblings are STARVING for attention, whether positive or negative. My 2 year old tends to act out if I don't play barbies with her.

My opinion is to ignore smart mouthed comments. If you ignore them, they will realize they aren't going to get any attention for behaving badly. Then treat them with kindness and offer to play games with them or something when they are acting nice. Or take them out for ice cream.

I have never spanked my 2 year old and she is a compassionate sweet little girl. When she has to go in timeout, I have her sit in her chair. I turn off the tv and she can't play with toys for 1-2 minutes. Then I tell her to come out of timeout. She instantly says "sorry mommy. sorry mommy. I love you" and then gives me a hug and a kiss.

She realizes that if I ignore her bad antics (showing her food in her mouth, or saying the word "stupid") then she won't get any attention.

Some acts are extremely reprehensible, hence why she goes in timeout. (for example she hit me in the eye with her dora doll the other week. She went in timeout for that)

Spankings are not the way to go in my opinion. I find it repulsive. Just try to keep your cool. If you have to, go outside and take some deep breaths to clear your head.

Kids can be extremely frustrating and just need guidance. I tend to explain everything to my two year old why she can't behave the way she does. Maybe it's not too late to do the same for your siblings.

Just my opinion.

TG~

I am sorry to hear that your sisters are in need of guidance. I think that as the adult big sister you have an oppurtunity to be a positive role-model for them. It is not easy to deal with children who are acting out, but if you can rise above it, and teach by example, this will speak louder that any shouting.
Since you are not allowed to discipline them when you babysit, why not set up your own incentive plan. Start each girl out with 'X' amount of prizes (this could be anything from quarters, candy, small toys ect...) When they act innapropriately, you calmly and quietly take one item from their stash. No arguments. If they do argue, you take another. This worked wonders the year I home-schooled my oldest daughter. We would butt-heads over everything, until I set up the system. She started working so hard to keep all of her items for the day! It will work even better with two girls as they will probably compete for the most prizes. Delayed gratification doesn't work all the time for younger kids, so seeing their goodies all set out (and consequently taken away) works better than telling them "If your good, I'll take you for a treat later"
This is just a suggestion, you may come up with a better idea. Remember though that you have an impact on these girls. You can help them to grow up to be likeable, enjoyable people! Sisters are for life, and this relationship you have with them is too precious not to work on!
Good luck,
Scaredy Cat