Inherit the Darkness — Willo Davis Roberts

Thomasina and Timothy were twins, although they didn't look at all alike. But from earliest childhood there was something... special... about them. Whenever one was hurt, the other would feel the same pain... and suffer the same consequences. It made no difference whether they were close, or apart; if one was injured, or severally depressed, or worried, the other knew, positively and without doubt.

Even when the family had to separate, after the twins' fourteenth birthday, Tommie and Tim did not grow apart; although they lived in separate homes, their minds developed as one. And now Tim was in terrible danger, desperately hurt. Could Tommie find him before it was to late...before they both must die?