Why does it say "b'Yado"?
Radak #1: They were in his Reshus to do his command, to pull Yirmeyah from the pit. This is like "Anshei ha'Milchamah Asher b'Yadeinu" (Bamidbar 31:49).
Radak #2: He pulled each with his hands to go with him. They refused to go, due to their weakness.
What are "Beloyei Sechavos"?
Rashi: They are worn, tattered clothes.
Radak: They are pieces of clothing dragged with the feet. The same applies to "Beloyei Melachim." They are ruined due to being worn out. Also "Eretz Melechah" 17:6] is ruined. Baluy is an adjective.
What are "Melachim"?
Rashi: It is an expression of decay, like "ke'Ashan Nimlachu" (Yeshayah 51:6).
Radak: Refer to 38:11:2:2.