Why in “If she joined this group of scientists, there would be people here who would understand her” after “who” is the word “would understand”, and in “What would they think about people who judged them” after “who” is the word “judged”?

Question

Answer

Because your first example is a second conditional structure predicting a hypothetical result.

Answer

In the first example, 'understand' is future in relation to 'join the group'. If you think of it as a command it is: Join this group because people WILL understand you here. So 'will understand' is being made conditional, not just 'understand'. In the second example, only 'judge' is conditional.