I hadn't thought about and i might be the odd one out but I don't think it's that weird or should cause any mum guilt
Styling is part of both of their work, in some ways it's like an additional/extended office space. I think if it was a man and the room was being used as a for a mix of his interests and primary source of the family income (for example gym if a PT, or a studio if they dabbled or worked in music) nobody would have the same problem with it.
Fashion and clothes are a multi-billion pound industry employing millions and she's a cog in that machine, styling is how she makes her money but because it's generally regarded as a woman's interest thing, beneath even being a hobby.
They also have the kitchen and second sitting room as work spaces admittedly, but the whole downstairs is play space for the children also; it's not like they're playing independently in their rooms at 3 months and 2/3 years old (in my experience of being around toddlers anyway). Personal space is important as you get older but family time and learning to be around other people is important when you are little, and if using the rooms like that is what makes sense for the family right now fair play to them.