If a revert faces pressure from family for things about Islam, specifically the pants being above ankles and the beard, to what extent does the rule of no obedience in disobedience to Allāh, apply? When is it that doing this haram act is better, the early sahaba’s struggles are inspiring though.

In everything, there is no obedience to somebody in disobedience to Allah. However, there are exceptions when something is life-threatening, or it is a dire situation and an emergency where you have no other choice. As for some harm, some problems, this and that: you can handle that, insha'Allah. You can be patient, make dua, depend on Allah, and do your best to persevere. Show Allah your sincerity and overcome these problems, insha'Allah, and they will go away. Very much your own family, the ones that used to give you problems, will start changing themselves, insha'Allah. They will come and ask you about the religion, and they will consider what is haram and what is halal, and so on. Keep making dua, be patient, and try to obey Allah to the best of your ability.