Hard to say. Its popularity could be influenced by factors like the plot, art style, and marketing. Maybe it's a hit among some specific groups of manga enthusiasts.
I'm not sure which book you're referring to because you didn't provide enough information. However, it was not common for a mother and daughter to like a man together because such a plot might be considered too romantic or inappropriate. In real life, a mother and daughter liking the same man together could lead to family breakdown, moral problems, and legal problems. If you have a specific novel title or plot, please provide more information. I will try my best to help you.
To draw like in manhwa, start by observing the style closely. Notice how they handle facial features, hair, and clothing folds. Then, try to replicate those techniques through consistent practice and experimentation. Don't be afraid to make mistakes and keep improving.
I'm afraid it's not easy to find it for free legally. Usually, you need to subscribe to legitimate manga platforms to enjoy it properly and support the creators.
You might find it by searching for the specific title on the Tumangaonline website. Sometimes, it could be categorized under popular or recently updated sections.