C.,
From a very young age children express the same motives that drive us throughout our lives; and, as we grow older, we typically develop increased finesse in expressing these motives. Sounds like your son is beginning to experiment with manipulating you to get what he wants - MORE of your time. As another respondent observed, this may be due to the time required by your special needs daughter; but that may not be a large factor. Most first-borns (or older children) who have younger siblings enter the scene do manifest some behaviors that are aimed at refocusing their parent's attention on solely upon them.
It is important to show you son "singular" affection and attention at times, to minimize his feelings of competition with his younger sister. And K. B's advice is wonderful: (1) make the behavior that you expect clear to him; and (2) lovingly enforce your expectations.
Caring parents develop their behavioral expectations based upon the physical health and safety of their children - as well as intellectual, emotional and spiritual development. You are just at the beginning of having your child (children) experiment with getting his way. The sooner that you develop the art of clearly stating and lovingly enforcing your parental expectations, the less time the kids will have to hone their manipulation skills.
It is also GREAT that you have realized that you put "words in his mouth" when he adopted the term "the octopus lady." It is a constant challenge to "listen for understanding" and not to contribute entirely different concepts to another's perceptions (this even happens when interacting with our spouses, not just the kids.) By focussing on our own listening skills, we can get to the real issues without contributing to them.
Perhaps these Bible verses will encourage you (especially the first one, since you really need some sleep! lol):
Proverbs 29:17 - "Discipline your son, and he will give you peace; he will bring delight to your soul."
Colossians 3:22 - "Children, obey your parents in everything, for this pleases the Lord."
Ephesians 6:2-3 - "Honor your father and mother—which is the first commandment with a promise—that it may go well with you and that you may enjoy long life on the earth."
God Bless You All,
K.