Some of this will depend on how challenging the classes you're taking are. For general education classes, the workload can be "all over the map" - some of them are very straightforward, but some of them can entail quite a bit of work.
One thing you could do is to try to get the syllabus of the courses you're considering in advance to see how much work it is. You'll probably want to talk to an advisor to go over it with you, though, just to get a sense of how much time it might take you. You could also start by taking on or two courses to see how it goes so that you can get a better sense of how much work it entails. (It can actually be really hard to come up with accurate estimates if you haven't taken a college course yet, especially if the course is in an unfamiliar topic; in that case, you probably won't know enough to know what you don't know yet).
In general, I recommend not taking so many classes if you can avoid it (especially once you get into your major classes). That's close to a full-time courseload along with a full-time job and a family. I've gotten several degrees part time (currently working on my third); from my experience, taking one class at a time is more than enough - if you take several while you're working full-time, that's all you'll be doing.
In order to be able to successfully finish your degree, you need to find a pace that you can actually sustain for several years - otherwise you'll burn out and not finish.
Ultimately, you only have 24 hours in a day. You need to know your limits and make sure that you don't exceed them.
I also suggest trying to schedule out blocks of time to study. Personally, whenever I get an assignment, I typically try to think about "when am I going to do this?" The more specific you can get with this the better - that will help you manage your time better, and it'll also help you not procrastinate. "I'll do this sometime this week" - bad. "I'll do this on Tuesday night right after I put the kids to bed" - good. (There was a study on this recently by Dr. Timothy Pychyl at Carleton University, but I don't have the citation; he refers to this as an "implementation intention" and found that it helps people reduce procrastination, even if they didn't rank particularly high in self-reported procrastination to begin with).