You can do both quests, but as usual, you have to first return one breadcrumb (A Turtle's Invitation) without doing any of the following quests, and then you can go back to get the other breadcrumb quest (An Illegible Scroll).
Maybe the breadcrumbs were all available at the beginning of BoA, I have seen the same claim for Fort Daelin breadcrumbs (Trouble at Fort Daelin, Helping Out, Somewhere Else, Bauer Backup), but only 2 are available at once, and you have to go back for the third one.
Interestringly, this method didn't work in Tiragarde Sound breadcrumbs for Thovas Base-Camp (A Letter to the League, Drust in Time) and for Norwington Estate (The Norwington Festival, The Glory of the Hunt)