For your cousin, get them Kitchen Table Tarot by Melissa Cynova.
I’ve recommended this to probably 30 people at this point and it’s the one they actually finish reading. It’s like 288 pages, doesn’t talk down to you, and the humor makes card meanings stick.
Cynova’s been reading professionally since ‘89 so she knows what actually matters when you’re starting out versus all the stuff that just confuses people.
The other option is The Ultimate Guide to Tarot which @Sploots already linked above. Fantastic if they want something more visual and comprehensive. Shows cards in different life contexts, which helps when you’re trying to figure out if the Three of Cups is about your friend group or your work team.
It’s got zodiac and numerology stuff too that they can ignore at first, then come back to later.
Skip anything that starts with Qabalah or says “advanced” on the cover for beginners. They’ll just feel dumb and quit. You want them doing actual readings within the first week, not memorizing correspondences.
For you at intermediate level - Holistic Tarot by Benebell Wen is basically the encyclopedia.
900 pages. Wouldn’t get that one for a beginner unless they like strong coffee. It’s technically marketed as beginner, but that’s crazy. You need to already know your cards to get anything from it.
It has everything. though. Astrology for all 78 cards, spread design, and professional stuff if you ever go that direction.
21 Ways to Read a Tarot Card by Mary K. Greer is also a great staple for anyone.
More about technique instead of meanings. It teaches you to trust yourself and read without constantly checking a book (which is usually the intermediate-term goal). That’s the bridge from beginner to someone able to give consistent readings.