Don't say:
Oliver cares about (cares for) his brother's investments.

Say:
Oliver takes care of his brother's investments.

Note:
Avoid also such expressions as: (1) He doesn't care for my advice, (2) He doesn't care for his work, (3) He took no care of him, (4) No one cared for him during his illness. Say: (1) He pays no attention to my advice, (2) He takes rro care over his work, (3) He took no notice of him, (4) No one took care of him during his ilfness.