Secure Memorable Passwords for Older Users
I'm not sure there is an answer at all. If a password is memorable it is either simple, contains a pattern, or has connections to other memories, thus making it less strong. Most suggestions I've seen use one or more of these methods.
You are specifically asking after memorable passwords, but why not use a password manager? Or a physical access token?
It could be as simple as using their smartphone for authentication, though then the smartphone has to be secured (and older people might not have/want a smartphone). If they happen to have one that has a fingerprint reader, it might be a good option. Still, giving them a separate device is more akin to a physical key and they might take better care of it security-wise.
And if all else fails, a password manager on their computer might be a lot more secure than whatever they can and care to remember, even if that one has a simple access code.
relatives [...] hate the idea of passwords
Relatives are maybe slightly different (I generalized up till now). Do they do important work, or are they janitors somewhere? Do they have a separate working laptop and personal laptop? What sort of services do they use?
All those questions change things. If they have some manager function and don't have a separate personal laptop, it might be a good idea to up their security and pay that extra dollar to get them a Yubikey or something. Which services they use also matters then: not everything supports 2FA (or what we're after in this case: 1FA after eliminating the password, or after making it rather weak). You might have to switch services, or use a password manager instead (or additionally, or use the access token for your password manager, or...).
There are lots of options, but I'd look at things people don't necessarily have to remember. We're after authenticating physical people after all, not filling their brains with something as difficult as possible.