Looking at the photos, I think it is best to follow Obelixx's advice and clear out the pots and put in fresh loam-based compost with added grit. Even the 'surviving' shrub looks quite ill. The one that has lost nearly all its leaves may need some trimming back later in the year, depending on what grows once it gets warmer.
Olives can do well with no feeding, provided they get good drainage and a loam base soil. I suspect your shrubs are water logged and sitting in damp claggy multi purpose compost. A feed like Vitax Q4 would only be a temporary solution.
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Olives can do well with no feeding, provided they get good drainage and a loam base soil. I suspect your shrubs are water logged and sitting in damp claggy multi purpose compost. A feed like Vitax Q4 would only be a temporary solution.