We have a window seat and no one uses it.
It gets used for storage. (underneath). For me, an actual sofa/love seat is much more comfortable.... because it has a backrest. Which a window seat does NOT necessarily have. NO one, uses our window seat. It is useless.
And, once a window seat is built-in, because it is built-in, you can't reconfigure it or the room, if you want. Later. Unless you tear out the window seat.
Window seats, are to me, mostly a quaint thing, in our imaginations. But it is not used a lot. If at all.
For 'chairs'... I would get, chairs that are real comfy that you can lounge in and curl up in. Not hard chairs. But nice and comfy upholstered chairs. Then people will be more prone to using it. And with an ottoman.
For seating, you have to get enough, so that if the entire family is in the room at the same time, that you all have someplace to sit.
Or, you can get nice floor pillows too and an area rug.
I don't know what kind of flooring you have in that room.