Already stated before, everyone except the slowest Squad at C3 is probably the "easiest" way, but to add one further detail: make sure that at least one of the teams taking the bottom path is faster than the two going north from C3 and the one starting at C1. The last thing you want is to finish the map without any team reaching the bosses at node 6 (yes, i guarantee it's very annoying).

Since it also has to kill Node 4 (and possibly Node 2 as well) it needs to pack some power, so an option is to use a fast Helper unit (used an Helper with evolved Wydler Orchid myself). If you have evolved Orchid... send her on the lower path. Or use her in a SLOW unit.

If your strongest team seems too fast (imo, anything above 500 risks finishing the map too early, unless they die against the final boss) and your girl selection doesn't allow for much flexibility, you can deploy Squad 1 (strongest, fast) to C2 (yes, C2.), slowest team to C1, and the other two teams + a slow Helper to C3 (so the Helper will go North, and hopefully kill the boss).

Imo, best bet would having Squad 1 & Squad 3 (both tough and slow) deploy at C3 together with Squad 2 and Helper (fast, tough - will take care of lower path + Boss @6), while Squad 4 deploys at C1 - so you have two chances at top Boss, but might or might not be possible depending on your girls.

And finally... Good luck. You'll need it.