So my group is currently playing trollfens, the second quest is a swamp map where all waters tiles require a strength/awereness roll to avoid being immobilized.

A situation came up where one hero became immobilized and then a second hero entered the same space and he to failed his test, now obviously he cant become immobilized in the same space since two figures cant occopy the same space but we could not find an aswer to what would happen in this situation...

I was playing this quest recently and thought about the same situation coming up. It did not however come up while playing. The way i thought about playing it if it did come up is that the hero who's turn it is would place their hero in an adjacent space of their choice(as its that heroes turn thus he gets to choose which position to place the figure into). This is as the rules explicitly state that a hero can not end a movement action in a space occupied by another figure - the only other reasonable alternative is to do what i said above.

I was playing this quest recently and thought about the same situation coming up. It did not however come up while playing. The way i thought about playing it if it did come up is that the hero who's turn it is would place their hero in an adjacent space of their choice(as its that heroes turn thus he gets to choose which position to place the figure into). This is as the rules explicitly state that a hero can not end a movement action in a space occupied by another figure - the only other reasonable alternative is to do what i said above.

That is actually exactly how we ended up playing it

When we played it and it happend we just let the secound player stay in the space he entered from (seem the most logic)