I agree with almost everything you said. There are only a few points that I would add:
1. Linguistic convention has no moral implications. Acting as if they did is what I call the "fallacy of appeal to negative connotation". Even if 99% of people call a fetus a person, and call abortion murder, that still doesn't make it immoral. It is a disingenuous appeal to emotion to bring up these words and people should be called out on it. Personhood in the philosophical sense is a very specific concept, and it is by definition the quality that grants an entity the same _moral_ status as a born child. Personhood matters in this sense only. In the colloquial sense of "most people refer to this as person", it doesn't matter at all. This is yet another reason for us to distance ourselves from words like "person" and "murder". The question is: when does a fetus become worthy of moral consideration?
2. The house analogy works up to a certain point, but it breaks down as soon as we acknowledge that sentience is a necessary condition for moral consideration. Although I do agree that we owe more or less morally towards a creature depending on the complexity of their conscious experience, I do think there is a sharp boundary between a creature with no consciousness at all and one with some consciousness, no matter how simple and rudimentary. I cannot imagine how things could be otherwise. I believe it is very safe to assume a 1-week embryo has no sentience at all, and somewhat safe to assume that a 24-week fetus with no brain waves has no sentience at all, but after that things get murky. Given our best knowledge it seems fetuses remain in a state of sleep up until birth, so it might be the case that their first subjective experience happens at the moment of birth, but it could also be that at some rudimentary level it starts earlier. Still, even if at some point we have reason to believe that at week 35 there is a sharp transition from no experience at all to some very rudimentary level of sentience, still the moral status that being deserves might be closer to that of a house fly than that of a conscious human child.