I only have one, and raising one is very difficult. I've heard from multiple sources that babies will play with each other and comfort each other, so I think twins might actually be pretty easy. However, I'm sure it depends on the age as well. When they're newborns, you'll have a lot more difficulty because they're just blobs that need boobs and diapers changed all the time. Around six months, then they might start interacting with each other and comforting each other more. However, it depends on their personalities. Some kids will hit each other too much to leave them to their own devices.
I read this in university as part of my human development course, and it gave me a huge leg up on parenting:
I read this more recently:
In the few cultures who still live a mostly hunter-gatherer lifestyle, children start wandering away from their parents to gather around 3, and older children take care of younger children so the parents can reproduce again. In more modern cultures with school and stuff, human fertility drops because the parents can't push as much responsibility onto their children. However, infant mortality can be as high as 50% in places without modern medicine, so if human fertility didn't drop in response to modernization, then we'd be at risk of overpopulation.
When they are first born, they wake up every 2-3 hours. You lose track of day and night since they don't seem to care what time it is. Very slowly, you regain your sanity as the child develops a sense of day and night. The financial difficulty will depend on if you breastfeed or formula feed. Breastfeeding and formula feeding are equally draining, and if your milk comes in late and you need to do both for a few weeks, you better have a partner helping you out because preparing formula while your baby is screaming with hunger sucks. Getting the water to the right temperature is a feat in and of itself. Then, you have to clean the stupid bottles and artificial nipples afterwards. I've heard that some mothers have an oversupply of breastmilk, but that wasn't the case for me at all. I had to work for it. We never gave him formula after 2 months, though.
If you put them in a cage, they stand there holding the edge and screaming at you while you're trying to brush your teeth. That really does a number on your brain. It's far easier on you psychologically to install the cabinet locks and safety outlets. Leave one or two cabinets with safe stuff such as linens and unbreakable containers unlocked so they can explore. We didn't bother smoothing out edges, though. Kid gets a few bumps and bruises, but that's how they learn to be more careful and aware of their surroundings.
Also, wear the kid when you need to get stuff done. Wraps can be a pain in the ass to put on and adjust while the kid is screaming at you, so I recommend a modern baby carrier with buckles.
If they're in a really good mood, they'll play independently for about five minutes a day, like the baby in this video experiencing occasional inattention: