Alice was about 20 when the Curse hit, and about 10 when she returned from WL the first time.
So if Grace was about 10 when the Curse hit, she had to have been born around the time that Alice came back from WL.
Which would mean that if RQ is Grace’s mother and Alice’s sister, there’s probably about a 10 year age gap between RQ and Alice.
The actresses playing Alice and RQ are less than a year apart in age. Though I guess RQ has magic, so could probably keep herself looking young if she really wanted to?