I think they're old enough for the truth:
You need them to go to sleep without you staying in the room (so you can get some things done) and they need to sleep in their own beds so they get a good night's sleep. Ask for their input on what they would like.
I also think that you need to separate reading from falling asleep. The stories are to wind down but when they're over, then they can turn on some soft music and go to sleep. My kids would be awake for hours on end just to hear the end of the story!
This is what we did when we made the transition from their falling asleep with us in the room to their falling asleep on their own:
(We never actually read them to sleep. We'd read stories, put them to bed, and then stay in the room reading/working on a laptop until they were asleep).
The first night we stayed 15-20 minutes in their room, then we left. After we left, we set the timer for increasing intervals: 2 minutes, 5 minutes, 10 min, 15 min, 20, etc and checked on them. We kept doing that until they were asleep.
The second night we stay 10-15 minutes, then left. After we left we set the timer for increasing intervals.
The third we stayed 5-10 minutes, left, and set the timer for increasing intervals.
The fourth, we stayed 2-3 minutes, left, set the timer.
After that we stayed a couple minutes, left, set the timer. We used the timer for a good 6 months before they didn't need us to come check on them anymore. They needed the reassurance that we were there and that we hadn't forgotten them.
We sometimes had to be quite firm and very calm in bringing them back to their beds. Occasionally we started the timer over when they were out of bed too much. We leave a light on in their room (they both read to themselves before they fall asleep; dd would look at books before she could read). We leave a light on in the hall and their doors open, so they can hear us.
If you notice, I've stated all of this as "we". My dh and I split the bedtime duties. I think the problem you've got is that your dh does the bedtime 'occasionally'. He really needs to become part of the routine. Dh and I alternate nights: 2 nights on, 2 nights off. It gets messed up sometimes (dh's out of town right now, and so I'm doing 4 nights in a row; next week I have a work commitment that will mess up the routine), but overall it works well. 2 on/2 off seems to be better than every other night, because we can remember it better and get a bit of a flow going. You could do a week on/week off, or 4 days or whatever.
The thing is, when it's my night, dh backs off. When it's his night, I do the same. For you, you may have to leave the house, go for a walk, hide in your bedroom or do whatever it takes for your dh to be able to have the authority and get into his own routine with them. I don't know whether it's worth working on getting them into their own beds first, and daddy being part of the routine later, or both at once.
The only other advice I can give is to be really really really boring when they get up/want you back, etc. etc. Take them back to bed, say goodnight and leave. Right now it seems they've learned that drama gets them more of momma. You're going to have to withstand a fair amount of drama to get a new habit established. They're 5 and 7. They're not infants. They can handle falling asleep on their own, especially if it's been preceded by snuggle time and reading. You're going to have to be prepared to be tired for a week or so while you hold firm. Remember that it takes 21 days or more to establish a new habit.
Finally, lest I sound like the meanest parent in the world, our kids do wake at night. If they do, they come in and sleep on the floor in our room if they want. The deal is: They have to sleep on the floor (my old bones can't handle it), and they can't wake us up (i.e. no screaming/crying, unless there's a reason (nightmare)). They just slip in, put their pillow and blanket down and go back to sleep. (It took a while to get that established with dd -- she'd lie in her bed and scream for us.) Dd has come in every night for the past 9-10 months. Ds went through about a year where he came in every night. No, we don't actually have a big bedroom. Yes, I step on dd when I get up to go to the bathroom, and dh steps on ds. They don't seem to mind.