13
Flames of Liberation lecture on Baathism: https://www.youtube.com/watch?v=ufJzwzdM8sE
Baath of Iraq Self-Crit on problems with their relationships with Nasserism, the CP, and the Kurdish movements: https://www.marxists.org/history/iraq/baath/index.htm
The split is seemingly bigger than it really is. Nasserists are viewed by the Baath as too focused on Arab state power, disregarding the non-Arab groups (like the Kurds) and differences between Arab nationalities (Syria and Iraq have much more complex polities than Egypt). The Baath of Syria split with the Iraqi branch due to ideological differences in trying to understand class dynamics (they are very different, and Syria is much more complex). The Communists in the region had a weak line on the Israel Question due to influence of French and English CPs. None of this was unbridgeable and much of it was bridged, but due to circumstances on the ground and miscommunications and opportunism, there was a lot of violence to these struggles which all sides regret.
As for Yemen I'm not sure what the differences were, it'd be best to seek out the writings of the groups involved during that period. I'm going to conjecture that MLs in power have similar views to the Baathists as Scientific Socialists, that they sought to develop their specific place as a bastion of anti-Imperialism rather than a utopian immediate Unity that disregards the concrete, specifics.