Marathon Training Plan for the time poor?

cj4kids

I started running about 6 months ago, and can now comfortably run 17-18k on a Saturday morning. I go to a spin class once a week, and try and fit in another run of up to an hour during the week too.
I am a healthy weight and feel very healthy in myself now, having lost over 19kg (and am under a kilo away from my end goal!).
I was planning on doing a half-marathon at the start of June (I did it once before before kids, 7 years ago), but my husband got me thinking about whether I should go for the full-marathon. I always thought a full marathon was a bit of a crazy idea, but I also like a challenge!
I know very little about 'proper' training, and realistically, as a part-time working mum to 4 preschoolers, adding more exercise sessions into my week is not going to happen, I have to work hard to fit in what I do now, and I have no time during the day without kids or work, so I fit exercise in early morning at the weekends, or in the evenings after work and kids are in bed.
So, for those who do know a bit about training plans, would it be possible/sensible to train say doing one hour long run during the week, which I could increase in intensity over time, and one long run at the weekend, which I could increase in duration. Plus my spin class which I fit in after work one day, and a few dog and children walks in amongst it all? I run where I live, which is hilly, and the marathon itself is on the flat.
Or should I just stick with the half-marathon, which I know I could confidently do without stress?

edited 'cos I just realised most of you are probably doing this in miles and I'm in New Zealand and we're metric - a marathon is 42kms, so I guess I am running a little over 1/3 of a marathon on a regular basis now, around 9-10 miles?