Any help finding this story would be appreciated.
Two sisters getting saved by their loner brother:
"Unlikely Protector" by Daghda Jim:
https://storiesonline.net/s/55910/an-unlikely-protector
https://storiesonline.net/a/Daghda_Jim/2
Not a nerd/loner saving his sister and a friend:
Marsh Alien's "A Stitch in Time":
https://storiesonline.net/s/50906/a-stitch-in-time
https://storiesonline.net/a/Marsh_Alien