Yes, definitely don't put your friends and family on the Pixelfed app right now - if they're not tech-savvy or particularly motivated, it'll be a disaster. I tried it and people got a terrible impression of the whole Fediverse because the app doesn't work well and the web version has other serious bugs that ruin the Fediverse's spirit and promises. Vernissage.photo might be an option for people who enjoy photography, but I haven't tested it on a smartphone. (Vernissage is similar to Pixelfed but has extra features and a different design).
If people you know will experiment with the Fediverse using an app, it's the UI/UX of the third-party app that matters, not the platform you pick. For example, if your mum only wants to write a short message and attach a photo, it doesn't matter if it's Mastodon or Friendica, because it's the app's UX that will shape her experience. So, if the interface is the most important thing for you, you should focus on finding a good third-party app. Whether her account is on Mastodon, Friendica, Sharkey, etc. won't make a difference, unless she connects via the web version. The Sharkey software, for example, has a very nice interface, but if you use the Mastodon app to connect to it, you won't see all of Sharkey's cute features.
But I think that if you're going to propose it to families with children, Friendica might be the best choice. With Friendica, you can create a private family group to share photos with specific people only. You can create photo albums. It's not that beautiful, but it works.
If none of these previous instances proposed here work for you, send me a DM and I might have a last option.