Hello Janet, thanks for replying!
"Penelope" seems to have been handed down our side of the tree as well, and I do think it must come from Penelope (Lunt) Crawley. I'm confident that Penelope is Phoebe's mother - her baptism record confirms it.
Mary's will mentions two of Phoebe Crawley's children - Phoebe Hales and William Williams. Both received £200 worth of annuity stocks. I'm not sure why only those two were mentioned, but I think Mary was particularly close to certain of her nieces and nephews, and left money to them.
This is still very much a work in progress for me, but I have made some progress since posting my query. I'll send you a message with some more information.