1)
What is the meaning of "va'Yasobu"?
1.
Radak: They surrounded him [to strike him].
2)
Why were 10 spears cast into him (apart from what entered his heart)?
1.
Pirkei d'R. Eliezer (52): This was for transgressing Kivud Av v'Em, which is like transgressing Aseres ha'Dibros.
2.
Radak (14, citing Sotah 9b): It is because he had Bi'ah with 10 concubines of his father.