Problem with spawn at airfield (Single Player)

I set up a mission where I wanted to have a squadron take off for a single player mission.

I inserted 12 planes and the first waypoint is marked as take-off on the field I want them to take off from. For this plane group I marked that they shall spawn as parked (I don't know if this is the word used in the English version of the fmb). They spawn nicely on the spots as indicated as spawn points on the map.

Now I have several problems:

1. But unfortunately two of them spawn in the German hangars for single engine planes and immediately explode. I fear that they spawn exactly on gras ground while the hangar is slightly above ground so that this leads to a collision making the planes explode. These hangars come with the channel map and have NOT been inserted by me.

2. A couple of seconds later all other planes except the player plane and two others just vanish. The remaining two start their engines.

3. And then do nothing.

4. Except the one that dips its nose into the ground as if it just accelerated without releasing its brakes.

What am I doing wrong?