In the first grade classroom I worked with, several of the kids were delayed. In some cases their parents refused any sort of testing, so they did not get any special help. Some of these kids ended up being held back so they could develop and catch up with their peers. Given the sometimes 2+ year age range in the same classroom the younger kids need additional time, as they are just not as old and developed as their peers.
Do you have a pre-first level in your district? That is popular around here in school district, it is after kindergarten and before first grade. It gives kids extra help and time to catch up before first grade.
Could you put him in some sort of summer school or tutoring program? Could he have an aid to help him work in the classroom during the year? Has he been tested to see if he has specific issues?
You say he always needs someone around at home to supervise or help him do things. I would try and spend time to help him become more independent and do things on his own. Or give him ways to have safe experiences where he has the power and says what to do.
Go for a walk have him tell you where to go.
Tell him to do something you know that he can handle. Set a timer and tell him you expect him to have completed it by the time the timer goes off. Sit near by but do something else. Keep repeating this with different activities each time getting further away until you are no longer in the same room as him.
Praise him when he does things independently. Give him time to play on his own. During this time his brothers and everyone else leaves him alone. Start with a few minutes and then increase the time.
As for tying shoes, he will get it eventually. When I was in kindergarten, we learned to tie our shoes with a half inch rope that we tied around our legs. We sat down on the rope with rope ends on both sides of us. Then they had us learn to tie with the big rope. We also learned to tie with two loops instead of one loop and wrapping around.
Good luck! Just remember everyone develops at different rates and lots of kids struggle with a variety of things throughout the years. Some kids are super gifted in some areas and struggle their whole lives with other things. Some seem to have an easy time of everything. Others struggle with everything. Some do not seem to struggle on the outside but are still struggling inside. Everyone is different and needs to learn to best cope with their strengths and weaknesses. Sometimes there are tricks and tips that can help people deal with their uniqueness and succeed in life. It is just a matter of finding what works. I wish you and Colby luck in the journey to figure out what works best for him.