http://www.golfclubatlas.com/forums2/index.php?board=1;action=display;threadid=27660;start=msg533019#msg533019That is the link to the South Bend CC thread. In my opinion its by far the best course in town and if you can work things out with Brian I would certainly recommend it. Its a beautiful site as well.
As far as the two public courses, it depends on what you like I think. Blackthorn is much wider and has some great holes, although it has a few odd ones too. Warren is very solid, old-looking, and very difficult. I've played both quite a few times, and would play Blackthorn if I only had one round between the two just because I think its more fun to play. Warren eats my lunch, so take that for what its worth. As Chris said, you'd have to really plan ahead to get on Warren most likely.
Angels Crossing is a good option too but with the family around I doubt you will want to drive that far. The original nine on campus is pretty dull, its flat without anything to distinguish it. If you want something that might be inexpensive and a quicker round try Erskine on the south side of town, great like old municipal course. It short, but the back nine is better than you'd expect. I wouldn't bring my clubs to play Juday Creek.
In terms of the weather in South Bend...who knows
You may get 70 and sunny and you might get 45 with some sideways rain and a lot of gloomy clouds. Most likely it will be somewhere halfway in between that, but the courses will be open and playable. If you get a decent day its a nice time to play (save for a lot of leaves on the ground).