Doubles (running twice a day) is generally really high mileage stuff (70+ miles per week). You normally see a hard/longer run in the AM and an easy recovery run in the afternoon/evening.

Best option would be to run it all in singles. If time really doesn't permit, then you can try some doubles. The problem is 4 miles + 4 miles doesn't really equal the benefits of an 8 miler.

Rather that chase mileage I would recommend that you chase time instead and let the mileage fall where it falls. I think 10 to 12 hours per week is about optimum so you could just aim to work your way in that direction. If you are training for a marathon you probably should be running 5 or 6 days a week. One day for rest is always good. Personally, I like doubles just to get the extra training time. If you try them work them in gradually and keep one of the runs real easy and limited to 30 or 40 minutes.

Wow, these are great ideas - although I've only just started on the full program. I'll keep them in mind!

The thing that helps me to get in the mileage is to put it on the schedule like everything else. I have a Google calendar that I use to keep track of all the family obligations and my runs are entered there just like a kids lacrosse game or a doctor's appointment. Make it a priority and it becomes a priority. This means that I get up between 4:30 and 5:00 AM every day, but it's a sacrifice I make willingly because of the returns that I get on it.

This ^^^.

I work full time shifts too, and I've got 3 kids under 5 (my hubby is the SAHD). And I work out what I need to do then plan it in over the week. I make it like an appointment. I start my early shift at 7am, so will get up at 0430 to run (usually) 10-12kms before work. But if that's too much or I'm running late, I'll happily take a 5k. I'm naturally a morning runner and find it easier to get up, pull on my running gear and get straight out. If I think about it too much then other stuff just takes over and I run out of time.
I've also found it useful to have a training schedule that I stick up on the fridge. I can see what I need to do over the course of the week, and I cross off what I've done when I've done it. I always get my long run in on a day off. Even if that means getting up at daft o'clock so I still have decent time with the family. If I can't run (either if the weather's crappy, I'm sore, or just can't be bothered), I have a cross trainer in the garage that I picked up for $20- 30 mins on that is better than nothing at all. And it's easy to go on there when the kid's having a nap or watching a dvd.
I think that as long as you mentally make the commitment, then you'll find ways to make it work. Also, find a training plan that suits you- some have you running and cross training 7 days a week. For most of us that is just not practical. My last training plan had me running for 5 days a week, and TBH I usually ended up skipping 1 day (at least). I've learned from that now, and I have a plan that has me running 4 days. my shorter runs are between 8-12km (60-90 mins for me).

good luck with finding what works for you.

ETA- The distances will depend where about in your training you are anyway, so I wouldn't worry too much about that. Just start at the beginning and it becomes easier to fit it in as you go along. this week my total distance will be about 45km. In 15 weeks time I'll be running 85km. Once the marathon is over, I intend to run 0km for a while!

I wanted to "ditto" those who said 60 miles per week is excessive for marathon taining. I run between 40 & 50 per week and my brother who has been doing this longer than me never runs over 40 per week. I did my first marathon training over a longer period so I could build mileage slower and run 20, 22 & 24 miles a few times prior to the race. Typical week in the last months would be 6mi/ 8mi/ 7mi/ 22mi/ 3mi.... thats a big week at 46 miles over 5 days on 2 days off. Anyone could get by on this or a little less.

Totally depends on what you goal for the marathon is. If you just want to get through it and have a good time, then you can surely do it on that mileage. If you want to actually race it and possible qualify for Boston, 40 miles per week isn't going to work. The caveat being if you have been doing 40 miles a week for 20 years, then you probably can.

Thanks! The RW plan that I modified yesterday has me starting around 20 miles this week (personal best) and peaking at 50 miles 3 weeks before the marathon.

That sounds like a good plan. I am a firm believer in high mileage if you are trying to run for performance. However, going high too fast is not good. Your next cycle you can start at 50 and peak as high as you like. By that time your body will be well adapted to the stress plus you will probably be running faster and it won't take so much time.

I have a second one planned 10 weeks later...

Be careful scheduling marathons that close together. The basic rule of thumb is one day recovery (not necessarily inactive, but not training) for every mile raced. So, you really should take at least a full week off after a marathon and then another 3 weeks of reduced mileage, easy running. Take two weeks off the other end to taper, and you are giving yourself 6 weeks to be ready for the next one. Not saying it can't be done, but exercise caution.