In writing for friends and family, you have a sympathetic audience, so just be yourself. Keep the writing simple and only use words that are part of your everyday vocabulary, otherwise it will sound false.
Don’t worry about spelling or grammar. The writing can always be tidied up later if required – it’s more important to record the memories at this stage.
If your grandmother or favourite uncle had written about their lives what would you want to read?
The answer is probably ‘everything’. Do likewise – after all, the fact that you remember details from 50, 60 or 70-plus years ago must mean something, and the smallest memories are often the most fascinating.
It’s best to show rather than tell. Instead of saying that Gran had a great sense of mischief, give the example of how she let you hide under her voluminous skirt when Mum was lurking with the bottle of cod liver oil. The reader will soon get the measure of Gran.
Paint a picture with words; describe colours, sounds and smells, record what your family looked like, what they wore, their favourite sayings and mannerisms. If you share feelings and aspirations your readers will empathise with you, but only include what you feel comfortable about.
Finally, enjoy your writing. If you enjoy it, it’s almost certain that others will too.