What pro- or anti-Yangist aspects do you think would be adopted by Mohism, Confucianism, and Daoism?
It's hard to come up with easy answers to this due to the limited resources we have (and the fact t that it has been years since I read anything of Yang Zhu). Daoism is also harder to address in this regard due to the extreme diversity of Daoist beliefs and the fact that Daoism already is extremely influenced by Yangism (although I do think there is one interesting conflict here).
To tackle a few areas...
Hedonism: Although in a more epicurean fashion, Yangism did use hedonistic logic to justify some of its principles. OTL, Confucianism often contrasted itself against the perceived asceticism of Buddhism (Daoism having less clear a position on this). In a "Yangism survival" tl, Confucianism is going to have to either embrace that logic to claim it achieves it better for political reasons, or push even further towards anti-hedonistic values. Daoism once again is hard to predict due to the extremes between ascetic cults and religiously motivated sex rituals etc. Mohism is going to contrast here less in terms Hedonism (in the context of being interested in pleasure) as much as the best way to be that, Yangism being in favour of Wei Wo "everything for myself" whilst the Mohists believed ultimately in equal distribution of material wealth.
Politically: pretty straightforward. Confucianism is going to have to get more had line in defending the position of the emperor against a political ideology which is fundamentally opposed to it as it did OTL. Mohism likewise may have to become more focused on political structure if Yangism is going to become its sparring partner. Obviously as well, Mohism, Confucianism and Daoism are all going to have to come up with more defences against the ethical egoism of the Yangist philosophy.
Theology/Theism: whilst we can't fully know what Yangisms position on many of these affairs were, it does seem fundamentally to have been uninterested in an afterlife/heaven (which I think would become a big focus for Mohism, something to the effect of "you may be enjoying life now, but those who follow heaven are going to enjoy the afterlife" in a way reminiscent of other religions) and was actively opposed to immortality on hedonistic principles, which is a key issue it has against Daoism.
OTL, what we now recognise as Daoism borrowed heavily as a fusion of Mohism and Yangism anyway, the Zhuangzi being essentially a combination of parallels of the two with the emptiness doctrine from Lao Zi combining the two.
Funnily enough, I could actually see a "Mahayana equivalent forming out of Daoism in such a Tl, having all the philosophical pressure for something like it to form. If a surviving Mohism is going to develop a grand, universe pervading epistemology and sense of self whilst Yangism continues its radical egoism, eventually some Daoist thinker is going to have to develop an intuitive epistemology to address emptiness in a similar fashion.
Note all of this is guessing without trying to go to far (also apologies for rambling), but here at least are themes I think could develop in such a world.