That's some going on the marathon!
I think alternating 6-8 week blocks would be best.
3 full-body sessions is plenty without any endurance work, so my preference would be to try a 3 day upper-lower split on top of what you are doing. 4 sessions is too much. That way you'll train everything once every 5 days and give yourself a decent chance of recovery. Just make sure you hammer the protein (1.5xLBM) particularly on weight training days.
Better to do too little and increase frequency or volume slowly than drive yourself into the ground prematurely, push very hard on the weights the last few weeks.
On endurance blocks, I think 2 full-body sessions will be enough for maintenance.
That's how I'd do it anyway. Good luck!