I can't open the link, but that sounds like the finest collection of old cobblers evermore. There is nothing in any text I can recall to suggest that they were anything but a pair of travellers who had got lost. What on earth would they be doing out stealing cattle at twelve o'clock o' the night O?

Regarding bereave, here's what the On-line Etymology Dictionary has to say.

"Old English bereafian "to deprive of, take away, seize, rob," from be + reafian "rob, plunder," from Proto-Germanic *raubojanan, from PIE *reup- "to snatch" (see rapid). A common Germanic formation (compare Old Frisian birava "despoil," Old Saxon biroban, Dutch berooven, Old High German biroubon, German berauben, Gothic biraubon). Since mid-17c., mostly in reference to life, hope, loved ones, and other immaterial possessions. Past tense forms bereaved and bereft have co-existed since 14c., now slightly differentiated in meaning, the former applied to loss of loved ones, the latter to circumstances."

IOW., if this source is correct, reiver is not the origin of bereave. Rather, the two appear to have sprung from a common Germanic root.

Interestingly enough the On-line Etymology Dictionary claims that the word blackmail stems not from the practice of reiving (which means stealing cattle), but from Scots freebooters who ran protection rackets against farmers. The word apparently comes from mal or male, meaning rent or tribute. Hence, blackmail would be unlawful tribute.