Hi Martijn -
Control Yafo gate: according to the rules you need to have all fortress/fort hexes. What if you have those, but don't control the TC? Would you have to give up the one fort that borders both areas, causing you to lose the control of Yafo Gate?
I think you would have to give up the Fort (R490), but you keep the Yafo Gate. Controlling the Yafo gate area prevents the Judaean from having an adjacent area to the Yafo Gate hex and thus retaining it.
When a ram stands on a breach hex and starts ramming the adjacent Fort, can the defenders attack the fort (apart from missile fire)?
I assume you mean "... can the attackers attack the Fort ...". In any case, the Fort may be attacked by the Ram on the Breach Table, Archers and Artillery on the Missile Table, and INF on the Melee Table. The INF pushing the Ram cannot attack on the Melee Table [11.3] from a Breach hex. As you note, Ram units may attack, but only through a GATE (not staircase) and only in response to a Sortie [11.14].
To enter a breach hex with a ram there have to be 2 connected breaches. Is this requirement only for entry? Could you leave the breach hex to a city area where only one breach gives access to? (and the other one to another city area)
I think so. The Rule [8.96] applies only to entry.
Must every unit in a hex attack the same hex, or could you divide the attacks on more than one hex? (both for combat and missile fire?)
You may divide attacks. For Missile Fire, Rule 9.7 [Mandatory Attacks] may restrict eligible targets. Melee is limited by Rule 11.1 [Eligible Attackers]. Note that 9.7 is only for Missile attacks. I think.