Quite a bit depends upon what is truly important to you. Video versus photography. Image quality versus price. Is this safari a once in a lifetime event and you want the best photos you can get with a willingness to up your budget a bit?
I cannot figure or your actual price range as I cannot duplicate your prices. Are those perhaps Euros? The R50V is $639 with the 14-30 from Canon is the lowest priced R50 kit that I can find and the R50 refurbished body only is $539 (Canon refurbished warranty is the same as if new). ZVE10 kit new is $800. So it seems you are looking at in the $800 range for cameras, then adding a diving housing, and nothing is in the $400 range. But if you have a source for an R50 for $400, especially if it has ANY lens, then by all means snag that deal.
How important is a safari camera? For the safari, you will want the longest zoom range that you can get. The Sigma 16-300 will be effectively a 25-480mm lens on the APS-C R50 sensor. For $800 that lens seems to be a good bet paired with a Canon APS-C sensor camera. I tend to recommend getting good lenses for your application first then the camera second. You could rent a camera and/or lens for your safari and buy a camera for family trips and live with less range. Or you could buy one used for $620 (price on MPB now) and sell it back after you get back and consider the ~$200 you might lose in selling it back as "rental". Getting great pics on your safari would likely be worth that to you.
A good dedicated diving housing is quite expensive and it's quite an investment considering you may want to change cameras. Getting a dedicated underwater camera or GoPro recorder might be an option to consider and deliver better value for you.
What are your priorities of video versus photography? The R50 vs R50v comes into play here and how much you would want an electronic viewfinder. Also, how portable and small do you want your camera? Do you want just a single lens or will multiples be ok?
So, some things for you to think about and let us know so that we can offer a little better advice.
