my trees,my land

[Juanita Letner]

concerned that the land at the creek will wash away because three trees were cut down. Also these people are disrespectful of boundaries, as they built a bridge on this land years before without permission when my dad didn't cause them any problem when they clearly knew the boundaries.

 

[KatDini]

And your question would be?
Sounds like Dad gave permission for the neighbors to build a bridge, as there was no protest or problem with it, per your post.

 

[adjusterjack]

concerned that the land at the creek will wash away because three trees were cut down.

Plant new trees or some other type of landscaping that will prevent erosion.

And if they cut down trees on your property, you sue them for the value of the trees.

Also these people are disrespectful of boundaries, as they built a bridge on this land years before without permission when my dad didn't cause them any problem

That's called "consent."

when they clearly knew the boundaries.

Do you read minds, now?

The solution to your problem is to put up a fence.