そうにないUnlikely to, Showing no signs of

ことに emphasizes a strong emotional or subjective reaction to an event, while そうにない expresses objective improbability. For example, 驚いたことに、巨人が負けた 'To my surprise, the Giants lost.' expresses emotional impact, whereas 雨は降りそうにない 'It doesn't look like it will rain.' simply states an unemotional likelihood.

そう expresses that something appears a certain way based on perception or indirect signs, e.g. 雨が降りそう ('It looks like it'll rain.'). In contrast, そうにない (or そうもない) indicates that something shows no signs of happening, e.g. 雨が降りそうにない ('It doesn't seem like it'll rain at all.').

そうもない and そうにない are extremely similar, both expressing that something is unlikely or shows no signs of happening. The difference is that そうもない feels stronger and more confident due to も adding emphasis, e.g. '雨が降りそうにない' vs. '雨が降りそうもない' (same meaning, but the latter sounds more confident).