Hi A.:
I have almost 5 month old twins who are going to the SAME thing right now. They were on the exact same sleep schedule until about 3 weeks ago then all TWINS broke loose.
Do you feed them both at the same time? I have been keeping their feedings on the same schedule but like yours, mine have different sleep patterns right now. As hard as it is, I usually just let them do their thing and if I have to go out then I gently wake the sleeping one and off we go. I figure 1 cranky baby is better than 2 cranky babies. Basically, while I let them get plenty of sleep, I make their day fit into MY priorities for the day. The only schedule I really work around is their feeding schedule.
It can feel very suffocating and overwhelming if you get the tag-teamed feeling. I think by just making mine tag along, they've become used to it and more readily go with the flow and the crankiness that I had in the beginning has gotten much better. One other thing I do plan is for long rides (we travel to the Cape and Maine quite often) by feeding them, etc. then heading out right after the feeding.
My suggestion is feed them at the same time and plan your schedule around feeding (not sleeping). It's not a perfect system, but it has been working out so far for my twins.
Keep us (or me) posted. I'd love to chat more if you'd like.
Take care,
R.