It seems like a long, narrow rectangular table might work well. Would a cradenza fit in front of the window?

So here's my suggestion...

Get a round adjustable height dining table that can be lowered to coffee table height.

Then get three curved upholstered bench seats. So when entertaining it's a conversation area. Raise the table and you can seat six for dining.

For family dining, keep one of the benches to the side wall and use chairs for the kiddos. The chairs could hang on the wall above the bench like art when not in use.

More pics...