DS1 is 3 and 8 months and the baby is now 8 months. By now, we are able to do a pretty smooth bedtime most days, not that we settled in a consistent routine but for any different situation that arises I already have the right fix or I am able to create a new fix then. I will share all the different thing that help.
First of all, I always try to put the baby down first, I nurse him lying down in bed, in this case DS1 will be : 1- by my side, while I read him whichever books he chooses or 2- still soaking and playing in the bathtub (small apartment) 3- with DH playing something quiet with soft lights (if DS1 wants because he generally wants to be in bed with us) 4- and only when I am exhausted or burnt out , watching animation of sweet books (goodnight moon, owl babies) in youtube on my phone or laptop in bed with us.
Then, if the baby doesn't fall asleep, oh oh: It will have already delayed DS1's bedtime due to me trying and trying and just wasting time. First of all: Deep breath! If DH is at home, it is no biggie. By then, the baby is nursed and may spend some good time with papa in the living room while I nurse DS1 to sleep. I may stumble on a very frustrated and cranky papa who feels his life is nothing but tending to family's needs and when he can finally do something by himself blablabla. Well so if DH is specially frustrated (he works a lot) or if he is not there (working evening) I will have the baby in bed with us while I nurse DS1 to sleep. Baby will be besides us: 1- being entertained by lil dolls, toys, rattles that I shake in front of him or, rough confession, (when he was very young specially ) being hypnotized by a phone app of a rattle that I held and shook for him to watch, a few more minutes of it and DS1 is out. 2- trying to reach for the same toys/dolls rattles as he got older 3- trying to catch different soft animals/balls that I throw back and forth (grabbing him by the foot when he decides to jump off bed 4- the newest thing, sitting in front of a box with different objects to hold, examine and mouth. (well, the baby is nursed when I start with DS2 so he is likely to be in a good mood, if he is cranky, he is either teething, for which he will take Camilia or he is sick then I will try whatever comfort he needs and/or nobody sleeps)
DS1 never sleeps with DH. It has to be me. I don't blame DH at all, This boy has more or less nursed to sleep for over 3 years now.
When DS1 doesn't fall asleep in the breast, we will hang out in bed, I may rub his back while I nurse the baby again. If baby doesn't want to nurse or/and DS1 can't fall asleep, the boys may "wrestle" in bed a bit and we start over. I may give up sleeping (deep breath again!) and trust that we can start over smoothly in 1/2 hour or so... bring the boys to clean DS1's room (in low light)... Deep breath!
In general, lots of deep breathing and patience, I myself will be sleepy and tired, nursing in a low lit environment can put me to sleep faster than the kids, so I tend to get cranky in the process when all attempts fail. Staying calm helps me find a new solution. There is lots of crying sometimes, from the children or even me. But those are happening rarely now.
When I bring either boy into the bedroom, the light is dim and I have put a few drops of lavender EO on a piece of wipe over our lamp.
Best routine: I bring DS2 in the bath with DS1, they love it. I wash the baby very quickly and bring him to our sleepy/lavender womb while DS1 stays playing in the bath. When he is done (he decides) DH takes him out, brushes his teeth... pee, pajama and he join us in bed. If DH is not there and baby sleeps before DS1 is done in the bath, it is heaven. If not, well... I am working on that one.
Counting DH out of the equation, helped me feeling calmer, It empowered me. I actually learn the best routines and felt the most patient when I didn't have DH around. Counting on him or adding his inability/frustration/whatever-it-is to the process just made things more messy. I found a place where he could help, he helps very little but it is a true priceless participation. Whether if it is fair, I don't know, but it works well this way (for our abilities and personalities).
You will get there and you may even like it more than before. Bed time can be a beautiful time for the family.