I think the two rules in the lesson are by and large those to remember:

when special emphasis on the body part is desired, or when another person is involved

This is effectively what you are saying.

Unfortunately I think "all bets are off" if we start to talk about poetry, where artistic licence will be the order of the day.

One could consider your Jacques Brel example to be a form of emphasis (I assume he is in love with someone and is making his point forcefully).

"La main dans la main" is effectively a direct translation of "hand in hand" (given that in French we are forced to provide the article), and almost by definition, only two people can hold hands so there is no ambiguity.

Honestly I wouldn't sweat this one. If you use possessive adjectives where you feel there is ambiguity, and nomral articles where you feel there is none, then that is good enough.

Michelle,

"When another person is involved" refers to the case when there are two people in the same sentence. So my understanding is that your sentence would normally use "les chaussures" since there is no-one else's shoes in that sentence to be confused with.

Even with your second point:

"Il se lave les pieds" and similarly

"Je lui lave les pieds" (I wash his/her feet).

I note that these reflexive verbs are not part of the discussion on the page you link to.

I'm not a native speaker so would be happy for an expert to correct anything I have got wrong here.

Months later but...this is one of those things that I just never fully "get". If I'm understanding this correctly this only applies when there are two or more people in the sentence AND there is no reflexive. So basically, only if there is no other way to avoid confusion when using la/le/les (such as a reflexive or the person's name when there are more people), would I use possessive articles. Other than if I want to place special emphasis (such as, I sank as low as having to wash someone's feet) or the body part is the subject of the verb. 

This one is definitely a source of frustration for me because in books and songs, there sometimes seems to be no rhyme or reason to it. Hearing real life usage of it just confuses me further instead of making things clearer.  I read "Je lave ses pieds de mes larmes" in a book of poetry. Françoise Hardy says "La main dans la main" and the French version of Pippi Longstocking uses this too. Yet Jacques Brel says "Ta main dans ma main". Yves Montant says "Car malgré son aigle au milieu du dos le cœur est bon et sous ses cheveux gris...".