How to say 孝 in English?
I would say that you are correct. The term &quot;filial piety&quot; is not widely known or commonly discussed in the US except when learning about Chinese culture specifically (perhaps Japanese and Korean culture as well, as they were strongly influenced by Chinese culture in the pre-modern era). The notion of &quot;devotion to family&quot; is much more accessible to a US audience and filial piety is not a familiar concept, so I'm not surprised Disney presented it this way, even though it is not correct.
In my experience, in English the meaning of 孝 is given as filial piety, which I understand to be a complicated concept with a long history involving respect for one's parents and elders in accordance with Confucian teachings and tradition, which entails certain duties, obligations, rituals, and modes of speech and behavior. In Chinese history classes I attended at my university in the US and in Chinese textbooks used at Chinese universities to teach foreign students Chinese, 孝 was discussed in the context of Confucianism and what it means for people to behave properly (ethically, even).

In the history class we briefly discussed 悌 as well.
The textbook used in one of the Chinese classes at 北京语言大学 I attended is 阶梯汉语·中级口语3. One of the new words taught in lesson 4 (p. 32) is 孝敬, whose meaning is given as &quot;present gifts to show one's respect&quot;

To get a sense for how this concept is understood in the West, here is an article from the Greater China Journal: Filial Piety (孝) in Chinese Culture.