Can you explain to them how much work (and time and money) is involved in making a quilt - and that you want to please them - but need more guidance as to what they mean.
I think the suggestion to let them select from patterns that you are willing to make is an excellent one. Then have them go fabric shopping (or picking, if they are going to shop your stash) WITH you. Changing the fabrics can give a different look to almost any pattern.
At the very minimum, ask them to give you some color combinations they like (Also the combinations they actively dislike!) Sometimes the colors help determine the style.
'Vintage' to some people can mean from 10 years ago - and when one considers how fashions and colors recycle, similar styles could have been from 40 or 70 years ago!
I think this quilt is an example of one that seems fairly easy to assemble, but changing the fabrics would give it a totally different look.
quiltingboard.com/pictures-f5/if-you-like-soft-colors-one-you-hot-off-machine-t201434.html