Learn how your stepfamily pronounces their last name. It’s their history, and now some of it’s yours.

Last names carry where people came from, and the way one is said is part of that, not a detail attached to it. Getting it permanently slightly wrong tells somebody you have filed them as a side arrangement rather than family. Learning it is a quiet way of saying you plan to stay.

Ask once, directly, and ask them to say it twice so you can hear where the stress falls. If there is a story behind it, where it comes from, what it used to mean, ask for that too. Few people mind being asked about their own name.