OK, from that I suggest you disband unwanted units like a few of those town watch, and recruit velites.
OK, you have segesta undersiege by the Gauls, what are the forces like/ your garrison?

Arretium/Ariminum under siege by Hannibal?

Is this some kind of a mod?

Where are you sieging carthage in Italy?

Wait, this is a mod isn't it. a united Rome? In this case forget about sieging Carthage, try to relieve a sige then you can use the fdreed up forces to relieve the other town. Forget about segesta. yeah you need vlites for ellies, lots of cav (4/5 units) will work wonders. Just try to wear them down and remember, once you have dealt with the two stacks plus beaten the Gauls back past the river, it will die down.