Just citing what they cite
You need to make an effort to get and understand the work related to yours. That is the only way you can make sure you are building on them, not misunderstanding. If you cite it, it means to me (as a reader) that you did use that work to reach your conclusions. You might get away with citing indirectly stuff you didn't check in detail, i.e., "Smith [19], summarizing previous work by Adam [1], Eve [2] and Noah [3, 6], states that...".