If you use GDAX, which is an exchange owned by Coinbase, you can convert your Bitcoin directly to Ether or Litecoin for free from BTC by placing a limit buy on the ETH/BTC or LTC/BTC order books.

Edit: However, it would probably be better if you convert your STEEM Dollars to Ethereum or Litecoin first, as they have significantly lower transaction fees compared to Bitcoin. From there you can convert to Bitcoin, Ether, or Litecoin as you wish using GDAX. If you were to use Coinbase, you would have to pay a fee on the buy and sell, which wouldn't be ideal.