Answer: The ivy will be a strong competitor for your new shrub planting, and could interfere with its rooting and establishment. For this reason you might want to try rejuvenating the existing shrubs rather than replanting -- at least the current shrubs have already established root systems. This assumes the existing shrubs are suited to the planting location in terms of amount of sunlight that reaches them.
Many shrubs can be renewed by correct pruning in late winter to early spring followed by top dressing of compost and possibly a general purpose granular fertilizer. How hard to prune depends on specifically what kind of shrub you have. Pulling the ivy away from the base of the shrubs and top dressing with compost (any time of year) can also help them to grow more vigorously.
To kill the ivy will probably take several attempts using an herbicide containing glyphosate. Late summer is a good time to apply it because the plants are storing root reserves in preparation for winter. Read and follow the label directions. You can also try to dig it out by the roots, then treat the regrowth with glyphosate.
Ivy can also be renewed. Mow it off short, top dress with compost, and new foliage will grow. The time to do that would be in the spring.
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