"Hum, hum, hum, HUM" and lyrics I don't understand

Last night, Number 2 and I went to a performance at the British Council. In celebration of Ramadan, the Council hosted a band (Eskendrella) and a choir (Upper Egypt Choir) who, performing in concert, sang various songs that everyone in the audience knew except we ignorant foreigners. The choir was composed mainly of teenagers who looked preternaturally cheerful for individuals of their age: they smiled a lot and wore almost-matching outfits without complaint.

The audience clapped and sang along with the songs. Somehow, magically, everyone seemed to know exactly when clapping was called for. Number 2 and I tried, but failed, to keep up. We also failed to understand most of the lyrics except those in one song during which the singers repeated the word "hum" for several minutes. That was a good song; they were rocking out.

I am getting more familiar with my new 'hood. Or, at least, I now know my way around the couple blocks of the main street in walking-distance from my apartment. I walk over to the gym, to the metro stop, and to the supermarket. The ability to walk to those three locations is a requirement for happiness.

Posted along the local main drag are several identical copies of this sign, all affixed to tree-trunks:

If there were just one sign like this I might write off the mistake as a mere (painted) typo. But someone obviously made a stencil to promote their purchasing of "every things" and then proceeded to carefully letter multiple, identical posters.

I am also intrigued by this advertisement for Reuben sandwiches at one of the local cafes.
Isn't the woman depicted Mrs. Doubtfire? Now what in the world has Mrs. Doubtfire to do with Reuben sandwiches? Are "sauerkraut" and "special ingredients" code for "cross-dressing"? Or maybe the message is that fathers-disguised-as-nannies will be crafting the sandwiches in the back? Perhaps I'm being to esoteric. Was Mrs. Doubtfire's real name "Reuben"?