I totally feel for you! I work and breastfed my daughter (still am actually, she almost 13 months), and I remember how stressful and crazy it was getting no sleep, pumping during the day, worrying about whether she would take a bottle or get enough milk. I can't imagine how tough it would be with two!
A few things that may help one is I was told to get this book by The Sleep Lady http://www.sleeplady.com/ which is awesome if you don't believe in the cry it out method or can't make that work - not that there's no crying involved here, but it's common sense stuff about consistency - she tells you exactly what to do and how to do it which helps me. She does phone consultations too, though that's expensive!
The other thing is, have you guys tried feeding the baby out of a cup or sippy cup? You have to do it with small gentle sips, or try the Nuby sippy cups with the soft tops. Your baby is younger than mine when she quite bottles (she was like 7 months) but she had been taking sips from a cup since 3 months). It's worth a shot!
Also, I'm not sure if anyone else mentioned this about the cereal, but you can put cereal in breast milk, it will not make it much thicker. Or it will, but only for a short period of time because the enzymes in the breastmilk digest the cereal. Try it with a bowl of rice cereal and you'll see what I mean. It will thicken up formula though. I know there's even a formula out there that already has the cereal mixed in -friends of ours got it from the pediatrician when their formula-fed baby had acid reflux. It's very expensive though. Although, my daughter refused formula - we would try to give it on occasion when we didn't feel like toting breastmilk places or if we ran out, and she just made faces and refused it.
As others said, hang in there and try to get a couple hours away from the craziness here or there (massage or pedicure?)to keep your sanity!