The Visioners - Into the Wilderness

Fourteen-year-old Joanna Clark, walking home from her London, England, school with her twin brother Samuel, is startled to find the family Volvo screeching to a halt beside them. The twins' mother, breathless with anger and worry, tells them that Dr. Cameron Stafford has just been released from prison in the United States, and that the family will soon be in great danger.
Whisked away by their mother to the family's remote refuge in a Welsh wilderness, the twins, their beloved border collie Flurry, and their aunt Martha are pursued by ski-masked gunmen sent by Dr. Stafford to kidnap and perhaps to murder everyone in the family for their role in sending him to prison years earlier.
The twins' narrow escapes and miraculous escapades, in company with 15-year-old Gareth Morgan (who seems to have a special interest in Joanna) lead them finally to confront Stafford himself in a final showdown in the wilderness.