Post-partum Depression but they’re not my kids?

So here’s a little backstory to help you better understand what I’m asking. Sorry it’s so long.

I babysit my sisters 4 kids full time & I’m currently 32 weeks with my first child. The children are 23 months old, 4 years old, 5 years old & 9 years old. I normally only have the 23 month old & the 4 year old all day because the older 2 are in school but there was a 2 week long vacation, then the week they went back to school they had a 3 day weekend & this week they had a 3 day weekend. You’d think things would get easier having the older ones around but it doesn’t. It makes it 1000% times worse. The 9 year old is very disrespectful & will literally fight me in everything & the 5 year old is a follower, so she sees her sister being disrespectful & starts in too which causes the 4 year old to do it as well. The 9 year old has had me so upset that I had contractions at 31 weeks. The 23 month old for the most part is an angel for a toddler if there ever was such a thing, but has type 1 diabetes we’re still trying to get under control. His insulin doses are still being moved around to see what works best. Depending on what his blood sugar is he can get very moody & just sit there & scream for the sake of screaming. So to put things bluntly & get straight to the point: I am completely in over my head. I am overwhelmed. Stressed out to the maximum.

I am to the point where I hate waking up in the morning. I cry because my alarm goes off & that means it’s time to get up & get the 5 year old & 9 year old off to school. I don’t want to look at the children & I feel like fucking monster because no one, especially a pregnant woman, should hate to even look in the general direction of their family. I’m a very family oriented person so to hear the words “I don’t even want to be around them” come out of my mouth last night when talking to my fiancé scared the ever living shit out of me & I know something is wrong with me. I don’t know if it’s just the stress or if it’s something like PPD. I wonder all the time how good of a mother I’ll be or if I can even handle the stress of a newborn if I can’t even handle 4 kids on my own. I love my daughter more than anything in the world but I’m terrified how I’ll handle having her AND babysit 4 kids at the same time.

I love my nieces & nephews & I hate that I feel so disconnected from them because we used to all have an amazing relationship before I started watching them. I couldn’t wait to come over & see them before this. & now I can’t wait to go home to get away...

Is it possible to have PPD even though your own child hasn’t even been born yet? I need help.