Choose the correct pronoun to complete the sentences:

1. (who / whom) should I send and (who / whom) will go with me?

2. The congregation enjoyed (them / their) playing the piano at the service.

3. Veterans Day honors our soldiers, for (who's / whose) sacrifice we must be grateful.

1. Whom should I send and who will go with me?

Think about this rule in terms of he/him--you would say "I should send him" and "he will go with me".

2. The congregation enjoyed their playing the piano at the service.

Playing in this sentence is a gerund, and a gerund is always preceded by a possessive pronoun.

3. Veterans Day honors our soldiers, for whose sacrifice we must be grateful.

Who's is a contraction for 'who is', which would not slot in and make sense in the sentence, 'whose' is possessive.