Well of course "all life is related." But when someone says to a NeoDarwinist, "Life comes only from life," probably he will be ridiculed. For the typical NeoDarwinist, it is "necessary" that life be the "emergent" property of matter.
Darwin's theory does not explain "life." Only "speciation." And only the sort of speciation that occurs on Terra. It is not a fundamental, universal theory of biology.
As for DNA, the similarity we see among creatures might have something to do with the fact that, evolution theory or no, what has been observed in nature (by, among others, Stephen Wolfram) is that there are surprising few "body plans" for biological entities. I believe the number he came up with was fourteen.
I don't know what a NeoDarwinist is, and please don't explain it. I don't care what it is, or what you think it is. That is an irrelevancy.
I know what Darwin was. He was a scientist, and a researcher.
I know what I am. I am a philosopher.
If someone tells me, "Life comes only from life," I equate that with saying "A is equal to A". Regardless of its truth or untruth, it leads nowhere.
It does not, for example, answer the question, "Where does life come from?"
For if you say, "Life comes only from life," then you haven't answered the question.
You are correct in saying that Darwin did not address this question. We would all be wiser to avoid it also.
However, life did have to come from somewhere. Even if you believe in Panspermia, that supposed extraterrestrial source of life had to have an origin also.
We don't know how, we don't know where. We don't know how long it took. But it only had to happen once.
Once it happened, life begat life. The rest is history ... or biology ... or archeology.