Learn Dutch: Jullie moeten deze verantwoordelijkheden delen. - You must share these responsibilities.

The singular is verantwoordelijkheid (responsibility). As you are learning in this lesson, abstract nouns ending in -heid have an irregular plural: the suffix changes to -heden.

Why is the long vowel sound in the -heden ending spelled with only one 'e'?

In Dutch spelling, if a long vowel is at the end of a syllable (an open syllable), you only write it with a single letter. So it is spelled -heden instead of with a double 'e'.

Why is the verb delen placed at the very end of the sentence?

This is because of the modal verb moeten (must). In Dutch, when you have a modal verb in the normal second position, it pushes the main action verb (delen, to share) to the very end of the clause.

Could I use dit instead of deze for this noun?

No, you must use deze. While dit means 'this' for singular het-words, deze is always used for 'these' with plural nouns, regardless of their gender in the singular.