When to use "by" or "to"?

The problem here is that visible and usable are not the same. Normally, you would use visible to and usable by:

stars visible to the naked eye
Merriam-Webster

Google Ngram:

Google Ngram:

However, since visible by is also acceptable, I would go with the less awkward combination:

visible and usable by all members.

rather than:

visible to and usable by all members.

I suppose:

visible and usable to all members.

is also grammatically correct, but it doesn't have exactly the same meaning: something is either usable or unusable (worthless) to me. If something is made available to me so I can use it, it becomes usable by me.

According to numerous examples in Reverso.context.net we should use only 'by' here. See one of the examples: 'Data for wood resource balances should be collected and analysis be carried out in close collaboration with the energy sector in such a way that the results be usable by all participants in the overall debate and work on renewable energy.'