I think you'll be able to do it. My pledgeship was a little hectic, but it wasn't too bad. We had weekly meetings (and we tried to schedule them around everyone's personal schedule.) and all house meetings plus other occasional stuff we had to do as a group. Plus pledgeship doesn't last too long, and I know at my house things settled down after initiation. I also have two sisters who took 18 credit hours AND worked way too many hours. LOL. They would miss chapter from time to time, but the house is accomodating. Your sisters will be supportive and will do the best they can to help you out. I say at least give it a shot!
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If the angels up above
Could hear us sing our song to you
They'd see that in our hearts
We're Pi Phi's from the start