This is a pretty good etiquette question. It'll be interesting to see the different responses. Ok to answer the question first, as you describe it....I would prolly just stand until told to be seated, just out of respect and I believe humbleness would not allow it to simply take a seat. I'm presuming that this is some sort of black tie event because of the tone set forth.
I've given this sort of thing a little thought before, and if John the Baptist was already seated but most others or Jesus had not yet, then I guess it's a reasonable assumption that He would sit at John the Baptists side at the head. So the thing to do would be to have a seat at the far side of the table on the side if bidden to just have a seat anywhere...so, to the far side because what makes me think that I would be seen honorable enough to go sit with John and Jesus?! So that's why I said I'd stand until told to be seated. Being able to be seated at the same table as our Lord Jesus, anywhere at the table would be a huge honor!
It is good to think on these things, and I hardly ever see people making an effort to have class or etiquette. Most people don't even know how to be a good listener! When one arrives somewhere and you walk into the room and the music is playing, and no one is talking....don't talk, listen. Wait until the piece is over and then talk. It's just polite thing to do. My dad taught me lots of little things like this, bless him! And you know what else? Scripture talks about this very subject. It's in Luke, I'll look it up...
It's in Luke 14.
I've actually called people on the not being a good listener and remaining quiet when you enter and they're listening to music, have some class buddy! I got mocked for it!, and that's ok because his dad just didn't know these things.
I don't know it all, lol. I was over 50 years old already before I ever even heard of a White tie event! I thought Black tie was the best, not so! White tie is. I would think that an event that the Lord is hosting would be White tie?