Must adiyen observe asaucam when a married daughter of a Dasaratra Gyati (Kinsmen where 10 days of asaucam is applicable) from four or five generations before, attains Paramapadam? If so, how many days? Having become aware that one of the siblings must observe asaucam, is it a Dharma not to inform that sibling about that asaucam, especially if the sibling has already planned for and preparing to conduct a Kalyana Utsavam to fulfill a prayer?

There is no asaucam when a daughter of Dasaratra Gyati attains Paramapadam.
At times, based on the place and time, it is better not to inform about an asaucam. When someone has set about to fulfill an important prayer, one must not inform the other about the asaucam. We must physically remove ourselves from that place. When we are nearby, we are obligated to inform about the asaucam, hence it is better to move away. Asaucam is applicable only when one comes to be aware of the incident that caused asaucam. If we are not aware, no asaucam. If one is not informed about asaucam, it does not taint.