Can one have type 1 and type 2 diabetes at the same time?

No, you cannot. Type 1 means your body does not produce any insulin at all.
Type 2 means that your body produces insulin but it does not take care of the glucose as well as it should.

Type 1 always requires the person to be dependent on insulin injections.
Type 2 can sometimes be controlled with only diet and exercise.

Yes you can. It’s called double diabetes.

Seems like if you have type 2 which progresse to type 1 (insulin-dependent) that it is on a spectrum.

Type 2 will never develop to type 1. They are 2 separate diseases that are only linked due to the high blood sugar levels. The causes are completely different.

Type 1 is an autoimmune disease where the body attacks the insulin producing cells in the pancreas.

Type 2 is where the body has become resistant to insulin due to the diet being so poor. It can progress to the point where the patient needs additional insulin as well as drugs to maintain health blood glucose levels. Type 2 can be reversed (often completely) with diet (a very extreme diet that most people can’t manage but still).

Type 2 can never be “reversed” per se. I mean, it doesn’t “go away”. It just means you don’t have to take any medications or insulin. You probably still have to get blood tests for blood sugar every so often. And if you fall off that diet/exercise wagon it will “come back”.

Also “double diabetes” is where your body can become resistant to the insulin you inject. So it’s kinda similar to type 2 in that way. But it’s not your body’s insulin that’s part of the equation, because it doesn’t make any in type 1.

Type 2 may end up requiring Insulin as in Type 1, but it is still producing insulin on it’s own as well.