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Very simple answer. Yes off course you should keep two separate blogs/facebook pages/websites for each niche.
But a great idea would be to keep both facebook pages separate and have another 3rd facebook page or group for to combine these two subjects. But make sure you submit such a content that is some how common or feels common in both of your businesses. That page or group will definitely enhance your both subjects/businesses. Try to add some interesting and funny content. People love to share with their friend with this is something interesting and funny. Hence this way your both websites will be promoted along with the shared content.
If this new 3rd Common page goes good, then you can stop perusing your previous 2 pages and focus on this SINGLE page. But more is better, you can maintain 3 pages and get multiple benefits. But all depends on your time and availability.
You can also hire somebody else for this work.