I would scale this WAY BACK unless you have a strong family tradition of everyone traveling a long distance for every occasion. I agree that a 1 year old has no clue what is going on, and usually they get so over-stressed by all the hoopla and the crowds that it winds up being a big disappointment for the parents! You will be working so hard, entertaining constantly, serving food, spending a fortune, and so on. Are you also having some of these people stay in your home since they come from far away? If so, you will have extra meals, laundry, entertainment, and so on. Your child will be surrounded by people she doesn't know, and you will be inviting people (the cousin's twins, the uncle's kids) who cannot handle big gatherings either. Two-year-olds do toddler things - they don't want to sit and watch a one-year-old get a bunch of toys they can't play with. And the 2 "tweens" aren't going to find this sort of thing fun at all - which may be why they act up. In big crowds, individuals don't get noticed - so yes, they have to be the center of things. And you will be fighting with this so that your child gets noticed on her day. It's turning into a competition, not a fun event.
It's perfectly normal to want to celebrate your baby's milestones, and the first birthday is special as you see how far she has come from that wonderful day she was born. But does putting her in the center of the room and having everyone ooh and aaah over her actually make for a fun day for her? How are you going to get her to nap when she's overtired, if everyone is there?
So I would ask myself, "what is the goal of this party?" If it's to give your daughter a good time, then this is not going to work. If it's to have a lot of photos, decide whether you really think you will care about looking at these every year. Would it be just as much fun to give her a few toys, take some pics of her in a new outfit and maybe tasting a cupcake and being intrigued by a candle? Then post the photos on line so your relatives can see them. If you have her grandparents in the area, then including them will be nice. Have these other relatives from many states away even met your child? Is this going to be something that is really fun for them? Does your family have a big tradition of traveling for every birthday and acknowledging every milestone with gifts? Is this something you feel compelled to perpetuate? If you feel you will be disowned if you don't have a big party, you may have to go through with it. But if you are going to offend some people by not inviting them, then maybe it makes sense to "offend" everyone equally and not have this big extravaganza that, apparently, many people don't enjoy or know how to behave in!
When our child turned 1, we had an immediate family party with an ice cream cake & a candle, and gave him his gifts. He wanted to play with the first one he got so we didn't go overboard. We invited Grandma and a couple from across the street. We took pictures and video, and it was great. We kept every party fairly small after that - just a few friends starting when he turned 4, and just immediate/local family in the years before that.
If you are sending out invitations 4 months in advance, and this is what your family expects, maybe you need to have a conversation with a few people to see if they really all want to do this, or if they are as conflicted about it as you are.
Good luck.