I'm doing kind of the same thing - training for a tough two-day back-to-back century event in late September and a half marathon in October. I don't have a job or kids, so overtraining really isn't an issue for me, but I probably don't devote much more time to my training than you do.
What's your goal for these events? Just to finish? Is the century competitive, or tougher terrain than you're used to? Or can you just maintain on the bike, from where you are now, and meet your goal there?
Alternate days is working for me. The only strength work I'm doing is what I do in my aerobics classes, plus another session of Pilates or yoga. I take a good long time to stretch after each run, and I'm trying to get better about stretching after a ride. Neuromuscular work, I do a little now and then throughout the day, when I'm reading, working on the computer, or just not doing anything else. I would NOT consider your farm work to be "stretching"! But I think at this point in time you definitely don't want to do any strength work on top of that, as long as you're practicing healthy lifting and bending and using your core when you do your chores. Make time for stretching, foam roller and Thera-Cane - injury prevention is really important since you need to be building miles pretty quickly.
I don't think doing the "bricks" will help you, since you're not training for a tri or duathlon. If I were you, I'd opt for longer runs over a short run plus short ride, since it seems like running mileage is really what you need to focus on right now.
I'm doing my long ride and long run on successive days, with my recovery day after that. Back in the spring I think it was Wahine who confirmed that that's a good way to do it.
Ack, you've made me realize how little time I have left to train. 
Also how little time I have left to be "under 50" which was the motivator for all this to begin with.
Speed comes from what you put behind you. - Judi Ketteler