Edo, I suppose it depends on how much money you want to spend on the party. There are rooms at Salty’s, but gonna cost you. There is a do it yourself placew above Big Al’s Brewery…two ends of the spectrum. I would suggest calling around…or cater it yourself and try a place like the senior center.
Here’s a wacky suggestion for you: The West Seattle Golf Course has a banquet room and they do provide catering. Lovely view of the golf course, easy to get to from the WS bridge.