One thing that helps a lot when introducing another child into the family is setting aside a regular scheduled alone time for the oldest child that they can count on. Children are usually fascinated with a newborn baby. Once those babies start to take on their unique personality, things start to change. The babies don't necessarily want to be poked or prodded. Maybe they're looking at something and don't want their older sibling to swoop in for a kiss. Maybe they are starting to pull hair. Even the most understanding and loving child will not like this. Eventually, there will be squabbles. If your older child or children know that they will regularly have you to themselves, even if it is for 15 minutes a day, they will not feel as though they've lost something. And, you won't have lost them, either. When they can depend on that time, you can encourage them to talk to you about their feelings. Yes, they love their sibling but they don't like ____, or they miss ____. Those things may often seem trivial to us but are important to them. If you know what those lost things are, you can often bring them back. Sooner or later, your baby will not want to share you, adding yet another spice. They will also need time when they have you to themselves. Meanwhile, they both will keep growing by leaps and bounds, with each of them bringing home new challenges. But, in spite of the challenges that go along with multiple children, they also grow up having each other, whether or not they get along. My brother and I didn't particularly like each other, but we could always depend on each other.
If you have more than one child, things often take more than twice as long. I expected, when I had my second child, that it would take longer to leave the house than it had with one child, but I didn't anticipate the number of things that could go wrong at one time. I had a terrible reputation for always being late. My friends teased me. My husband and my next partner teased me. Even my children, as they got older, teased me. Feeling exasperated, I would try to explain the numbers of delays caused by others that led to my being late ... We were all dressed and ready to go when the baby vomited everywhere. Then, someone else had an accident. Walking out the door, suddenly I had to change a leaking diaper. These days, I don't have children living with me anymore and am rarely late. I did learn to plan differently, though. I often had everything packed and ready to go the night before an outing so that I wouldn't be scrambling around more than necessary. I would even pack the car the night before, being sure that I already had my diaper bag, snacks, water or other things I might need. The kids were asleep, and I could think about what needed to go with us without distraction. That became so much a part of my routine that I still do it today.
When I had my first child, my housekeeping changed. I couldn't keep up with everything I had to do and also keep my home immaculate. When my second child came, my house was in chaos. I quickly learned to prioritize, constantly shifting to accomodate that chaos. I always felt that creativity and fun were important. My kids had access to all kinds of messy things to learn and create with. Spending time with them was also important. I struggled with juggling both of those important things and still getting my work done. I found lots of shortcuts like creating contained areas for messy play, or sending them outdoors with their mess. That made the clean-up easier. I also invested in various containers for different toys. Legos in one box and the train set in another, puzzles in a drawer, action figures in a bin, dolls in a basket, etc. They would bring out one or two at a time, and we would all put them away together. I even made a denim drawstring bag that opened up into a large square with a townscape of roads, buildings, a lake with a beach, a playground and more that I had made with iron on patches. The bag held their little cars and people. They played with the toys on this mat, then I just tied it back up when they were done. I also found that I could tolerate some mess if that meant I could also manage to have time for myself and for my partner.
In families, we all need to learn to work together, recognizing our weaknesses and strengths and capitalizing on them. We enjoy some things more than others and are better at certain tasks than others. Why don't each of us do what we love or do well? I always hated that concept of everyone being treated exactly the same. We're not the same. If this child loves films, I will take them to a movie. If that child loves dance, I will take them dancing. If they each get to do what they love with you, they shouldn't be jealous of their sibling. Although, some jealousy is inevitable. Birthdays were particularly hard in our family until I realized that I could enlist the aid of a sibling in the planning. It made them feel a part of the excitement. And the actual celebration went better without a jealous sibling whining and trying to sabatoge it.
It almost always boils down to that one all-important thing ... time. Each child needs time alone with each parent. They also need time to be only with their siblings, and each parent needs to take all of the kids by themselves and give their partner a break. Extended families are also a huge help. I loved spending time away without my brother. I had grandparents, aunts and uncles and cousins. The most important ingredient in all relationships (and I include the one with yourself) is making time for all of that. Good luck!