1)
Will he literally wear the Kesones and Avnet of Shevna?
1.
Radak: It is a metaphor. The Kesones is a garment of grandeur, and the Avnet is a belt on the loins - a sign of strength, that he will not falter from his grandeur.
2.
Malbim: No. The custom was to dress the appointees with an expensive sash and robe for grandeur - "va'Yalbesh Oso Bigdei Shesh" (Bereishis 41:42).
2)
How will he be a father to residents of Yerushalayim?
1.
Radak: He will be a faithful counselor and a good leader. This is like "va'Ysimeni l'Av l'Pharaoh" (Bereishis 45:8) - an advisor and leader of his nation.
2.
Malbim: He will have mercy on them like a father on his children; he will guide them in the straight path.