Hi Dellwell,
Whom,who,that are adjective clause pronoun used as the object of a verb, they are placed at the beginning of the clause.
The man "who(m) I saw was Mr .Jones.
In this sentence "WHO" is usually used instead of "WHOM", especially in speaking." WHOM" is generally used only in formal English.
"WHOSE" is used to show possession.
Example: I know the man.
His bicycle was stolen.
!
I know the man "whose bicycle" was stolen.
WHOSE usually modifies people, but it may also be used to modify things.
Like his,her,its and their,WHOSE is connected to a noun.
I hope this would help you make the difference between WHOM and WHOSE.
God bless.
Mintern.