There is not a problem combining ivy and heather. The brunt of the hot western sun may be a bit much for them but I would expect them to adjust to it unless a hot reflective wall is also contributing a bit too much intense sun and warmth. I suspect either droughty soil or poorly drained soil is the cause of that plant problem. Sudden changes in temperature such as a cold front could also be causing the problem.
Likewise I doubt the herb problem is due to two different plant species that don't get along. Herbs do love sun as a group, but some will tolerate some shade. If that eastern exposure gets at least a few hours of sun that should be enough to keep them going if not thriving. Check for moderate soil moisture in that planter also. You may want to remove the planting medium and replace it with a fresh, quality growing mix in case that is contributing to the problems. Many herbs can take some cool weather but many such as basil cannot.
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