I don't know what you are looking at. Sounds like some specialty mix instead of the chicken feed most of us are used to seeing. Those are just not standard.
Chick starter is usually betweeen 18% to 20% protein. I can't remember exactly. There is one for game birds that is around 24%. That is too strong for chickens.
Grower is 16% protein, which is usually recommended for about 6 weeks until you start layer feed.
Some stores do not carry starter and grower but instead have a combined starter/grower, 18% protein if I remember right. You can feed that from day 1 until you switch to layer feed. To me, this demonstrates it is not an exact science.
Some stores carry developer, which is 15% protein. This is recommended to replace grower for chicks from 13 weeks until they start to lay.
Layer is also 16% protein, but it has over 4% calcium, which the hens need for the egg shells once they start laying. The extra calcium can hurt growing chicks. The normal recommendation for layer is to start it at 20 weeks or when they start laying, whichever comes first. I don't understand the 16 weeks you mention to start layer. Kinda sounds like a local specialty feed mill.
These are not hard and fast, your chickens are going to be some kind of freaks if you don't follow this, type rules. These are guidelines. General suggestions. People violate these all the time and their chickens do OK. Part of these recommendations is that it is the most efficient way to get a laying flock to laying age healthy and prepared to be productive. With our small flocks, being off a few percent in efficiency is not that noticeable. In a commercial operation with a few houses with 10,000 laying hens in each, a few percent in efficiency means staying in business or going broke. Part of these recommendations is that in the first 6 weeks, the chick is growing and developing its body very fast. It is growing a complete set of feathers. It needs good food to get off to a good start. Then from 6 weeks until they are laying, the chick needs to slow down growing a bit. They will still go through two molts before they are adult and they will increase in size a bunch, but their body needs to grow more slowly as they mature internally. Their body needs to mature at a rate that matches their internal development. It is not that they will absolutely have problems if their bodies and their sexual maturity gets a bit out of whack, but that they can have problems.
With your 2, 4 and 7 week olds. There are lots of different things you can do. I'd probably keep the 4 and 7 week olds on starter another week, then switch them to grower. The middle group should be completely feathered out by then so a cut back in protein should not hurt their development noticeably. I don't think the older group will be hurt by being on the higher powered feed for another week. I think this is the best compromise looking at your way forward. As far as the 2 week olds, the ideal situation is to keep them separated and on starter until they are 6 weeks old, then switch to grower.
As I said, these are not hard and fast rules. If I run out of feed with a group that is 5 weeks old, I'll get a bag of grower then and switch. If I have starter left over when they reach 6 weeks, I keep feeding it until it's gone. If you want to, you can mix starter and grower so you can finish off a bag of starter. These are general guidelines. If you cannot or don't follow them exactly, no big deal. I just think it is a good idea to have a rough idea of what you are aiming for and why, then get somewhat close.
