The altcoins are largely pegged to bitcoin in terms of pricing. Not sure what you mean by stable here, I would suggest BTC and ETH , they are relatively stable coins. But otherwise there is nothing really stable as such in the crypto world.
Na, stablecoin is a tethered coin. It has to be tied to an asset.
That is really what defines them as stable coin, tied to an asset that is stable in price and preferably on something outside the cryptispace and it should always be audited to provide legitimacy and trust