I'm sure there are cases to be made for every family dynamic. Only child, two children with huge age gaps, one set of twins, etc. But I'm here to make the case for why having two siblings is the greatest blessing you'll ever have.
When you have two siblings, you have two people to learn from. If you have one sibling, you'll either do exactly what they do, or exactly the opposite of what they do. With two siblings, you get to watch them both trial and error in their own ways, and whether they are younger or older or on both sides, learning from two different people's successes and failures can be much more constructive than seeing more than two or just one.
When you have two siblings, you are able to relate your personal interests and beliefs into two different people. One sibling might be your go-to for advice and funny stories about relationships, and one sibling might be your go-to for music and stress. You don't have to throw all of your baggage on one person, and you don't have to force bonds that aren't there. You can split yourself among two people who have to be nice to you.
When you have two siblings, you have someone to go to when you're not getting along with the other one. If one sibling is being mean, as siblings do, you have another one to go to. You don't have to put all of your eggs in one basket. If one sibling doesn't want to hang out, you've got a back-up.
When you have two siblings, it is easy to divide your time between them, but also not get bored of just one. You don't have to feel like you need to write down concrete plans to get time in with all of your tons of siblings, but you also are able to change it up if you've been around one too much.
When you have two siblings, you get a chance to know and love people who are different than you in so many ways. You are able to empathize and understand the different ways people deal with stress and fear and joy and anxiety because you've had a lifetime of watching other two other people deal with everything in their own way.
When you have two siblings, you start to see them in you. You see the good and the bad of each of them inside you, realizing that having two amazing and frustrating, different and similar siblings has molded you into the person who you are today.
When you have two siblings, you have double the lessons, double the fights and most importantly, double the love.