Given that your father’s PD was diagnosed at age 88, it is possible that he has a form of parkinsonism known as “lower body Parkinsonism” in which the primary problem is with gait and balance and with lesser involvement of the arms and hands. It tends to occur in older individuals and doesn’t respond to dopamine replacement (ie levodopa/carbidopa). It would be important to know if his signs and symptoms slowness of movement, rigidity, and tremor improved with levodopa/carbidopa. If so then he likely does have Parkinson’s Disease despite the very late age of onset. If his symptoms haven’t gotten better on levodopa/carbidopa, then it is likely he has lower body parkinsonism. I suggest he have an MRI to determine if he has the neuroanatomical correlate of lower body parkinsonism, namely microvascular lesions in the sub-cortical white matter of the brain.
Regarding your question about vitamin B complexes, they are not an impediment to treatment. You should know that in the early days of levodopa therapy (1960s), before carbidopa was added to the formula, most of the drug would be metabolized in the gut and liver by an enzyme known as peripheral decarboxylase, that relied on vitamin B6 as a co-enzyme. To decrease the breakdown of levodopa by this enzyme, physicians recommended that patients taking levodopa avoid vitamin B6. However, ever since carbidopa was added to levodopa (brand name Sinemet) to interfere with the decarboxylation of levodopa, patients are able to take all the B vitamins without any difficulty.