M.R.
My husband and I had "dates" with our oldest when the second was born (they are 20 months apart and dates might be a quick run to the grocery store and a smoothie and McDonalds, etc.). I can't drive for a few more days since having our third, but he has been trying to take the two boys out and once I'm "better" I'll be ditching him with the baby once in a while to go "out" with the older boys together and maybe one-on-one.
Right now my husband's out with our 4-year-old for groceries but they were stopping at the library on the way to hang out in the kids' section.
My 4-year-old has started whining more and throwing weepy fits once in a while. It is terribly irritating and he is all of sudden needing to interact with me while playing (which he hasn't "needed" before), so I'm sure some of that is the baby. He is too big for me to pick up and snuggle, so I have to have him climb up on me on the couch and I really only hold the baby when I'm nursing or can't move to put him back down. It sounds like you're doing great and making the efforts that make sense with the older kids and the rest will just work itself out. Babies are boring for kids at first since all they have are needs and they don't even play yet. =)
Maybe if you don't already, make dinner with the older ones and reinforce that they are super helpful to YOU (not just the baby) and make that some more one-on-one time with them.