
Peach brandy is a fruit brandy distilled from fermented peaches — though the name is also used for grape brandy simply flavored with peach.
As the base it is hard to replace without changing the drink; apple brandy is the usual stand-in where the recipe calls for it by name. For a small accent a peach liqueur works — cut the sugar elsewhere, since it brings plenty.
Peach-flavored brandy
True peach brandy is distilled from peaches; "peach-flavored brandy" is grape brandy with peach flavoring added, usually sweetened. US labels allow both names, so the two are often sold and used interchangeably — and the flavored one will make a drink noticeably sweeter and less dry.
Peach liqueur / peach schnapps
A liqueur or schnapps is flavoring and sugar on a neutral base, markedly weaker. The drink comes out sweeter and softer: pour about half as much and drop the syrup from the build.