It's so easy to say "have your elderly loved one see a doctor at the earliest sign of memory loss." But how do you convince another family member to face the fact that she might have Alzheimer's?
It is too scary to contemplate being mentally compromised. Denial kicks in. People in denial over their memory loss will often make up reasons why they didn't know things, why they forgot. They may blame you, say that you never told them. Underneath the defensiveness is probably deep fear, conscious or not.
In general, it can help to suggest to the family member that "Many people ask their doctors for routine memory testing as they age and that they are smart to do this so that they can learn ways to slow inevitable memory loss." This can "normalize" getting tested so they feel comfortable doing so without having to admit that there may be something wrong with their memory.
Still, family members in denial will probably not be motivated to follow through on their own. Offering to accompany them can help. If it is your spouse who is having problems, make an appointment for both of you.
The way your family always copes with stress and communication is the way it will cope when someone starts losing their memory. This may or may not work well. But the courageous can always keep lovingly trying new ways and hoping for some small progress.