As of now, the Edens Zero manga is not finished. The story is still unfolding, and fans are eagerly awaiting the next installments. There's no definite end in sight for the moment.
I don't think it's a straightforward true story. Usually, such shows take liberties and combine various elements to make it more captivating. Maybe there are loose connections to reality, but it's not a pure retelling of actual events.
In general, sunbathing nude in public is not appropriate as it goes against social norms and decency. However, in some private and secluded areas where it is legal and not visible to the public, a mom might choose to sunbathe nude if she feels comfortable. But she should also consider the potential impact on others if accidentally seen, such as her children or neighbors.
There may not be a widely known 'nude family story' in the mainstream sense as the concept might be considered inappropriate or misinterpreted easily. However, there are some stories in the context of certain art movements where families have been depicted nude to convey deeper meanings such as innocence, unity, or the natural state of humanity. But these are more in the realm of art history rather than a common 'famous' story.
Swimming nude as a boy is not acceptable in most settings. Public places have rules about proper swimwear for a reason. It protects the privacy and comfort of others. Additionally, it can lead to various problems such as potential harm to one's own body from the elements or possible unwanted attention.
On a nude beach, proper behavior includes respecting the different body types and levels of comfort of others. Don't touch or approach others without permission. Additionally, make sure to bring and use appropriate sun protection as you would on any beach. The key is to create a harmonious and respectful atmosphere where everyone can relax and enjoy the beach experience in their own way.
One risk is sunburn in sensitive areas that may not be as exposed when wearing clothing. Also, there could be a risk of insect bites in unprotected areas. And if it's in a place where it's not supposed to be nude, there are legal risks of being charged with public indecency.