Alright:
1. pathing-markers are not too important, most maps should work fine without them.
2. what are the blue and red buff mechanics? I don´t know what you mean with that
3, the castle estates are indeed to small, which is a problem. why? because the game simply does not allow more than 4 players in multiplayer. above 4 you can only use AIs to add more players to the map. and those AIs, they need space.

also important to know:

The scenario-options (scripts) are not made for skirmish-maps but mission-maps where you have only 2 players. more than 2 players almost always create problems with any kind of scenarios, even in missions. why? because player 3 in the script for example don´t has to be player 3 in the actual game. he might be player 5 or whatever and therefore would get an invasion from player 3 instead of reinforcements for example. so basically you cannot script a multiplayer-map (at least with more than 2 players.)

and the person who asked you about redesigning the map probably also meant, that you clear the space around the spawnpoints from trees and stuff and set them further appart, so the AI can build a castle... because you always can play 1vs1 on every map anyway.

to summ it up: I would recommend to delete all of the scripts, most of them cannot work in any case. also I would redesign the map to a 2vs2 version, so the AI can build a castle and the map would also be ideal for multiplayer, because almost noone plays multiplayer with addional AIs... it is always 2vs2. there should be enough space for 2 players on each side, so you don´t have to change too much on the map to fix those issues. just select the spawnpoints one by one and change the size temporarly to the maximum with the mousewheel - if it stays white (and not turn black) on every level the AI has enough space.

@Bartelbi: About the building space!

There could be 3 solutions
1. Remaking the map in XL
This would be most intense considering the time I'd need.
2. Reducing player numbers
A possibility. But three players fits the three lanes best - so I would not like to do that.
3. Handling which would be to handle resources and space best. Building place is indeed sparse here. U got any ideas how I could change the playstyle on this map so it is not that focussed on building space and resources?

1, I would not remake the whole map, that is too much work indeed.
2, the idea with the three lanes will not work anyway. why? because only 2 player on each team can be real players, the 3. must be a AI. and AIs always attack which they are programmed to. thats different with everyone of them. the wolf for example always goes after the weakest, even if he is located far away. others attack the nearest, or randomly. so they will not use your lanes most likely.
3, changing the playstyle away from resources and buildings on a multiplayermap is not really functional, because both are of the essence in a strategy-game like that.
the only thing which might be possible is: not allow buildings at all and set a standing army for everyone. note: more than 1000 units on the map are not possible, so it would be max 250 for each player on a 2vs2. to be balanced everyone has to have exactly the same troops. but this does not work with the AI, so more than 4 players on the map would be impossible again.
could be fun in theory, because you would start with the battle immediately and the 2 players on each side would have to work together much more than in normal multiplayer maps. but there would be nothing to defend - no homebase, no fortress, no walls - exept your lord maybe and since everyone has the same troops, fighting might not make much sense. both parties would just create one big army and if they clash, the winner would be chosen through luck and not strategy most likely.

Hey bartelbi,
sorry - there was some time passed from when I started typing until posting, so I did not notice your first answer.

I thank you very much for the lot of information that u gave me, e.g. I didn't know about the scripting issues on MP Maps.

What I meant with red and blue buff mechanics is the following:
When starting to design a SHC2 Map looking like the battlefield that you're fighting on in League of Legends, I wanted to get max detail. There are four points on the map where special monsters are spawned (2x red, 2xblue, that is one of each in the top right half and the other two in the bottom left half) that reward you with a certain buff, when being killed. As something like this is not possible here, I decided to substitute them with village estates that grant reinforcements when being conquered. That would be some certain offensive troops for the red buff villages and some rather defensive support for the blue ones. But as it seems I can leave that idea out of the plan :(

Redesigning it for 2v2 would not be much of a prob, could do that soon!
Edit: I designed it 3v3 hoping they would finally fix that sh_t so 8 human players are possible again :( but I will bring up 2v2 as this is still not the case...

I think I will experiment a bit with different maps and scenarios. The idea of not allowing buildings and only having the battle seems fun to me too. Would be one of the alternative ways that am looking for!
Unless I would be able to implement a full MOBA Mod, I would not want to fully get away from gathering resources. My thought would rather be that players can save space because they get the recourses with - for example - quests. But that would bring up the scripting issues again :(