Complex sentence: They were bought by a pyrotechnics company, Pyrojunkies Ltd., while retaining the brand of Wells Fireworks; the ownership of Wells Fireworks has remained in the Dartford area of Kent.
Split into simpler sentences: They were bought by a pyrotechnics company, Pyrojunkies Ltd who have retained the brand of Wells Fireworks. The ownership of Wells Fireworks has therefore remained in the Dartford area of Kent.