solderiing 3 posts at once

[Embo]

Hi everyone,

I'm making a triangular cage and have hit a potential challenge. I'd really appreciate any tips/guidance please.

The triangle in the photo has some medium solder in it (I know it shouldn't but it's a long story!). I want to solder the 3 posts onto each point so my questions are:

1/ can i use easy solder on these and then extra easy when I'm fixing this triangle to the top triangle? I will also be soldering two tube set stones onto two external sides of the triangular cage which is also causing me to headscratch.
2/ how do I prevent the posts from toppling or moving with the flux when soldering?
3/ is there a way of soldering all 3 at the same time?

Thanks so much
Emmy