Lots of good feedback already. Agree with others saying push aside the
marathon for now and focus on setting realistic goals by running well at
shorter distances. The process and results need to be enjoyable if you are putting
in the time. And watch the diet.
I'd consider bumping up w/u and/or c/d on your tempo or progression to make
that your longest run. It's more time efficient that way. Introduce a day with
100-400m reps and hill surges of varying paces in place of the day you set
aside for the normal long run.
If you have access to cardio machines, I found 30-40 minutes twice a week
after kids go to bed are great for your days off from running. My primary go-to
evening basement sessions are the erg or treadmill incline power walking. I
found those to two workouts to be the most beneficial to running.
I dropped my mileage from 90-100 per week to 45-55 “training miles” (sum
of running + x-training equivalent) with a lot of success making some of those
tweaks. Married, three kids, full time job, coaching HS and youth sports, etc. –
not a lot of extra time. Long gone are the marathon days, but running
mid-distance races again has been a blast. Best of luck.