Dude, seriously. Two sieges at once? You'd better be able to close that place up entirely - that's the only way my current (human) fort has survived as long as it is
And nobody's going outside until the entire trade tunnel is filled with cage traps.
And even then!
*gonna catch three or four sieges and build them a pit, then remove the wall someday when I finally get bored*
I'm not sure that having them overlap and fight each other is possible right now; later when the Army Arc gets fleshed out better, maybe.
As far as wealth goes right now:
Pop. 19 (just got immigrants; was 20 before I offed a useless punk with pets)
Created wealth: 34300
Imported: 50056
Exported: 630
Probably not enough to warrant attack. As far as defense systems go, I'm working on a magma moat with a wildfire starting system integrated into it at four points.
Of course, it would be cowardly of me to seal the moat off completely, so I'll be making zig-zaggy floor bridges. That way, an archer or two can slow them down some before they get to the center.
For the record, I've deduced that axes are the best way to handle these buggers. Since most forms of organ damage (pain) won't slow them down, severed limbs and bisections/decapitations are the most assured means of stopping them. Barring that, hammers and maces to knock them into the moat, and possibly collapse bombs to splash them with magma.