So, what I would like to see addressed here is, first of all, how strong the indications are that current life has indeed exactly ONE common ancestor.
Imo, if abiogenesis is real (highly doubtful from a science perspective imo), then we can say biology evolves from chemistry (so to speak), but if that is the case, then embedded within the rules of chemistry is the ability to evolve biological life forms. Simple enough, but let's take the next step in logic.
Then, we can say there is a commonality within chemistry that is what gives rise to life.
So the fact all or most life forms share similarities, such as DNA, is not necessarily due to originating from a single biological life form, but can be due to the simple fact of sharing common origins in chemistry. In other words, if chemistry is predisposed to give rise to biology, then there is no reason not to expect these principles to keep working, again and again, and the fact there are wide similarities within all species is not evidence at all for common descent.
Of course, the other commonality that can explain similarity is that there is a Creator (sort of like how one can spot a picasso as oppossed to a Renior).
I think you aren't looking at the details enough. On another thread, anglehard posted the paper by Woese arguing for a progenote stating that is the only possible solution since the differences within the 3 primary kingdoms indicate the common ancestor to them could not have been simpler organization or some such.
Without getting too much into it, the fact is those differences don't fit well (and they are observed facts not speculation) with the idea of a common ancestor at all. They fit special creation and ID just fine, and can also fit the idea of multiple ancestors resulting from abiogenesis.
Of course, all of this leads to ID, not current mainstream evo models.
Also, note that evo claims of convergent evolution argue that different and similar forms arise via environmental pressures and so evos already refute ironically the claim that such similarities must be the result of a common ancestor.
Take DNA or actually any commonality. There is no reason at all to discount environmental aspects, is there, for these commonalities?
and yet lead to a single descendant family as we now observe.
We don't observe this. Don't want to nitpick but just point out the phrasing here can be a little overly suggestive that something is factual and observed rather than merely believed to be true.
As far as the theory, it is a nice story, but it's not really that verifiable; it doesn't really deal with the alternative; and it is unnecessary to explain current observation and ignores the interdependence factor. For example, the growth of some types of organisms enable more growth of others. More plants enables more plant eaters. There is no reason for one "family" line to exclude the other lines since it is not a zero sum game.
I asked for papers that seek to substantiate the theory of evolution as being true. This paper really doesn't do that, but it does raise a serious problem within evolutionary theory and offer a solution. I think the solution is probably untenable and thus the paper, imo, is more evidence against evolutionary theory than for it.