"Being forced together" is three words, but it does the job of a noun in this sentence. Another similar sentence with "noun + is ...ing" would be "illness is forcing couples apart" or "illness is making life difficult" only illness is one word, not three. Because the verb "to be" is doing the job of a noun in the sentence it must be in the -ing form, so here "being forced together" describes the situation of couples needing to live close together. This noun is the subject of the sentence. You could also write "being forced together is difficult" or "being forced together is no big problem". The word "how" at the front of the sentence is often used in the titles and headlines of texts that want to explain how something happens. If I wanted to write an article about fitness I could give it the title "How I stay fit" or "How to eat well". It's not a question! So the structure is: how + noun phrase + is doing something How learning English is making me cry. How living in this city is driving me crazy. etc.

Yeah. The things you can and can't say for uncountable nouns are a little inconsistent. You can't say "one intelligence", but you can double intelligence, add up intelligence and even calculate intelligence. Same for other uncountables: Learning a language takes double the effort needed to learn an instrument. If you add up all the energy you spend on it, it's a large amount. Sometimes it's hard to calculate the total time you need. As ever, the best example of an uncountable is rice. You can't ask for one rice (what is it? one bowl? one cup? one grain?) but you can certainly eat double the rice I do. If you want ;)