To clarify: You can give as much as you want up to $5.43 million lifetime limit without paying any taxes. If you keep all of your gifts to everyone under this amount over your lifetime, you will not pay any gift tax. The $14k limit is the amount you can give without reporting to the IRS and having it count against your $5.43 million limit. Thus, if you are a super generous person, if you kept your annual gifts to everyone under $14,000, you could theoretically give millions of dollars away without ever reporting.
If you are giving back $50,000 - you will report 50 - 14 = $36,000 to the IRS.
Your remaining lifetime limit across all gifts to all people is now $5,400,000 - 36,000 = $5,426,400.
Bottom line: you're doing a smart move since your sibling will get assets with a much better cost basis than you had, thus saving them a bunch of taxes. You will never have any taxes related to this transaction, but report anything over $14,000 on your tax form.