Father and Grandfather Anju
We don't know much about Ai-chan's Father and Grandfather.
Ai once mentioned that they were long dead.
She misses them very much but she overcomes her sadness by thinking how lucky she is to have Yuu, Hana and Hoshi.
By a dream we find out that Ai promised her Father not to let Yuu get overworked because of his sickness.
Which means that Ai knew her father, when she was little.^-^
About the Grandfather we only know that he's now buried with Grandmother under the earth.