"If I visit a US city for pleasure, but work on my business at the same time, am I violating immigration law?" -> technically yes. Practically no. The solution

"If I visit a US city for pleasure, but work on my business at the same time, am I violating immigration law?" -> technically yes. Practically no. The solution is to not "work" on your business, but "do business". If you're in the US and have meetings with clients, that's not considered "work" by immigration law. Just don't tell the immigration office you're going to "work". In practice your situation is totally fine.