They were probably talking about something completely different and completely legal. You used to be able to, and maybe still can, claim up to 99 dependents on your W4. That does not affect your taxes at all. It merely reduces the amount withheld from your income so you get more of your pay on payday but you still owe the same taxes on April 15th.
Dammit, Janet, I didn't want back... But, so much wrong with this...
If you do what you describe you will be paying penalties.
And illegally claiming non-dependents as a dependent is totally a real thing. Dependents will up the EIC and CTC, but you actually have to provide for your kids, not grandma or someone else.