The masculine plural definite article 'gli' shows that you mean 'the hobbies' when your topic is 'gli hobby' in Italian. It's pronounced 'lyee'. The masculine plural indefinite article 'degli' shows that you mean 'some hobbies' when your topic is 'degli hobby'. It's pronounced 'DEH-lyee'.
Cylinders.
boats
McDonald's
Martinez's
cobwebs
You wouldn't pluralize "processing", but you would pluralize "process" making more than one process "processes".
Handkerchiefs is correct.
No because on is an adjective, not a noun.
Sirs is the plural of sir
To pluralize the surname "Fourness," you would simply add an "es" to the end, making it "Fournesses."
The plural form of panic is panics.
leonardo dicaprios favorite hobby is making home videos