Well, to start off, Sobey's is the owner of Thrifty Foods, as confirmed by their about page.
Sobey's did buy Safeway, for $5.8Bn in 2013, however their website doesn't list it amongst their brands (see the footer), and various business news articles mention the selling of Safeway stores following intervention by the Competition Bureau in Canada.
Basic conclusion: Sobey's do indeed own both, but the acquistion of Safeway led to unforeseen regulatory problems, that may change the situation somewhat.