Answer:

You can certainly include both cardio and weights in the same session, though it is better to separate the two, especially when long distance is the goal. The reason is that weights and long-distance cardio are basically two completely opposing goals.

My recommendation for someone training for a marathon as a priority and with a time crunch would be 2 total-body weight sessions on their own days, with 4 running sessions on non-weight training days.

The marathon does require some very specific longer-distance training to properly prepare the body but weights can certainly help.

I just wouldn't combine them on the same day and would definitely have at least 1 full day or rest per week.