As for tandem feeding, have you tried the EZ-2-nurse breastfeeding pillow? It makes latching them on so much easier cos they balance without rolling off. It's much easier than with v-shaped pillows or pther supports.
Most breastfed babies don't last 4 hrs, so maybe you could try starting one feed a little earlier so the next baby doesn't go completely loopy by the time you get round to feeding them.
And basically, sit in front of the tv, remote, snack, drink and just feed them as much as you can. Let everyone else do the other stuff.
If you have to give a bottle of formula, then you have to. It's better to give the odd bottle than give up breastfeeding altogether! But there arguments for exclusive breastfeeding as I am sure you are aware of!
Personally I never bothered with expressing as found that so time consuming, time where i could actually be feeding my babies directly myself.
I really would give tandem feeding another shot! It could make all the difference. Place one baby on cushion, then the other, then latch one baby on followed by the other. Do the difficult feeder first (if you have one) so you can use both hands for that one. Then support the other baby under the shoulder blades, supported on pillow and let them throw head back when they open mouth, then shove them on quickly and definitely, before they shut their mouth again, with one hand!
Good luck, and remember to feel good about every breastfeed that you manage! You're doing them so much good!