Farden:
+4 for Endurance, and +5 because light riding horses get a +5 to Fort saves, according to the MM? I'd guess its because +2 for Con, and the rest +3 because a horse is a 3 HD animal with Fort being one of its good saves.
It's just a CON check, not a FORT save. Looks like it should be +6
Farden's horse ends up with 11,19,23,17 which is good enough to avoid any fatigue or damage.
I'll make 4 CON rolls at +6 against DC 10, 12, 14, and 16 for everyone's horses. For simplicity's sake lets assume that Moonlight, Mutt, Jeff, the cart horse, and the floating eye emerge from the ordeal unfatigued. If things get too bad for anyone's horse at any point, we'll assume that you guys dismount and finish off the 4 hour trip on foot to spare the horses.
Here are the results:
11,10,24,17 Glumr's horse takes 1D6 (1 point) damage during the second hour and becomes fatigued.
7,11,13,9 Just as twilight falls Holly's horse steps in a hole and injures itself. You all stop to check it out. (5 points of damage) The wound is bleeding, but there's no structural damage. Holly casts a cure minor wounds on her horse and you keep going. Sadly, things do not improve. The forced march in the dark is very hard on the horse. It takes another 5 points of damage over the next two hours. Holly decides to try a cure light wounds. (cures 6 of the horse's 9 points of damage) and refuses to ride the poor animal any further. You continue on foot. Holly gets a 4 on her DC 10 CON check. She takes 4 points of non-lethal damage and is fatigued from her 1 hour forced march.
This changes things slightly for Farden and Glumr's rolls. Farden gets just a +1 (12) on his DC 10 CON check, so he's OK. Glumr has endurance and gets a +4 (15) on his DC 10 CON check. They're both fine.
17,7,19,8 Mord's horse doesn't fare too well either. It takes 4 points of damage during the second hour and becomes fatigued. Much more shocking, the hour on foot tires the unstoppable Mord. (5 points of non-lethal damage and he becomes fatigued)
25,23,15,8 Snow's horse does fine, but the hour on foot tires her. (6 points of non-lethal damage and he becomes fatigued)
You're tired. Some of your horses are injured. You're still slogging through swampland in the hazy moonlight. The good news is you seem to have eluded the goblins. You slump down after midnight at the first reasonable chunk of ground and start your watches.