Learn Italian: Loro vendono la casa e ricevono i soldi. - They sell the house and receive the money.

They both come from regular -ere verbs: vendere (to sell) and ricevere (to receive). For regular -ere verbs, when you want to say 'they' do something, you drop the -ere and add the ending -ono.

Which syllable should I stress when pronouncing vendono and ricevono?

The stress falls on the root of the verb, not the ending! You should emphasize the first part: VEN-do-no and ri-CE-vo-no. A common beginner mistake is to stress the second-to-last syllable (like ven-DO-no), but for the 'they' form, the stress pushes back earlier in the word.

Why is it i soldi if the English translation is the singular phrase 'the money'?

In English, 'money' is treated as a singular, uncountable concept. In Italian, the word soldi is plural (historically referring to coins). Since it is a masculine plural noun, it takes the plural word for 'the', which is i.

Do I always have to use Loro when talking about what 'they' do?

Not at all! In Italian, you can usually drop the subject pronoun because the verb ending (like the -ono in vendono) already tells the listener who is doing the action. Simply saying Vendono la casa e ricevono i soldi is perfectly natural and very common.