It's kind of a "case by case" thing. When a situation came up I just worked w/ figuring out the best way to keep both babies happy. We spent lots of time on the floor. It's easier to be close to both babies when there's no worries about falling. So starting pretty early I set up a nursing station on the floor (w/ various configurations of twin nursing pillow, boppy(ies) and regular pillows). That way when one was done I could set her on the floor next to me & give her toys to play with, read to her, etc. while her sister finished nursing (or slept at the boob, which they both did lots of as babies. Now once they're asleep I can slide the pillow off my lap & let them sleep there on the floor (naps) or carry them up to bed (night). For diaper changes, I found it worked really well to use the changing table attachment for our pack n play. I'd put the other baby in the pack n play and that was she could see me & I could see her & talk to her while I was changing sister's diaper.
Ummm . . . they both really liked to "stand", being held up from a very early age so we started using doorway jumpers quite early because that was a way they could "stand" w/o me having to hold them, since I couldn't hold them both to stand at the same time. We put the doorway jumpers side-by-side in the double doorway into our bedroom & they could "talk" to each other & bounce toward each other & such in them. Those remained a hit for most of the first year (took them down when it was getting dangerous because they were bouncing so "hard").
As newborns, we went through a period where Lexie was fussy in the evening & needed to be carried laying stomach down on someone's arm. Ashlyn wasn't as fussy but wasn't content to be totally ignored during that time, so I figured out to pop Ashlyn in a sling (sitting facing out so she could see what was going on) before she got fussy, then carry Lexie on my arm & we'd go outside & do "laps" around our cul de sac until Daddy got home.
Once they were big enough for hip carry (which I started really early by snugging hte sling really tight up around their neck) I could carry them both (& nurse them both) in the slings so that helped, couldn't do much else while I had them both in slings, but at least had them both happy
Up until they got too big (around 16 mo I think), we "coslept" w/ dh at least starting out the night in the recliner part of our sofa holding one baby (he put pillows under his elbow & held baby cradled there while he leaned back & slept, he felt "safer" that way than having a baby flat in bed next to him where he might roll) & I'd take the otehr baby to bed w/ me. When "dh's baby" woke up to nurse he'd bring her up to me & (when they were tiny and would ONLY sleep touching someone) take the other one back down w/ him. Once they got older they would sleep ok just being in bed near us so then when "his baby" needed to nurse he'd just come up & we'd spend the rest of the night w/ all 4 of us in bed (queen bed w/ twin mattress "cosleeper" attached) - we'd start the night w/ the baby I had in the cosleeper & me right next to it in the regular bed, then when dh brought the 2nd baby up we'd put her in the middle of the regular bed & dh would sleep on the other side of her.
Those are the situations I can think of at the moment, hth