Look, Jarm, I know you're going to feel guilty about the other two whatever we say but it really is in your head and not theirs I'm sure. And you can assuage the guilt by letting yourself off the hook and doing whatever it takes to keep them happier and you BF. E.G Send out DH for big jar of jellybabies. Put on shelf next to sofa. Design sticky badge for each 'helper' to be taped onto jumper with sellotape. Tell them BF needs to be 'pumped' by helpers jumping up and down in the other room for 5 minutes each. Give jellybaby for each 5 minutes of jumping...
Or just go for the straight bribery: stickers on wallchart for each day of helping and at the end they get to go to the park/Legoland/Hamleys/Disneyland Paris (delete as budget allows)
The guilt won't go away. But YOU deserve this after how much you wanted it... AS Hunker says, you already know how much time you won't have sterilising, making up, warming etc bottles and then you'll STILL have to sit on the sofa for 40mins every couple of hours feeding, burping changing etc. It will make sod all difference...
You're having a bad patch: they come, they go. You knew it would be like this. Maybe your son is fussier than normal because he's having a growth spurt (how old is he?)
Your other girls do not hate you. You can guarantee the minute Father Xmas arrives, they'll have forgotten all about you and will get that glazed faraway look in their little eyes, dreaming of Mylittlepony land filled with Barbie princesses (or wotever girls do these days, I've only got blokes...)
Distract em with that (yeah - get Xmas decos up, that'll get em going!), give in to the tiredness (you go like this: yup, I'm exhausted, I can't fight it, I just have to get on while exhausted - it makes life easier to accept it IMHO. Same with the guilt) and tomorrow, or at the weekend, or next week, you'll feel better. I promise. And in a month, or two, you'll be back doing everything with those girls that you did before, just with a baby on your front (get a sling! babywear! handsfree!) and no bottles to lug around...