So, five things to start with:
Welcome to BA!
Please don’t double post - you are on moderation meaning your first ten posts have to be approved by a Mod before they appear, so please be patient and wait for them to show, it all depends on how busy the Mods are.
Please don’t use Upload sites that want money for their services, use pasteall.org/blend - its free, run by the same guys as this website and doesn’t bombard me with adverts…
Your cannot bone parent one object to two bones - you need to add a bone to do the job, linked to other bones to keep it in place.
I don’t have time before I go on my hols to explain everything that is wrong with your armature…
But this is how you do a parallelogram rig in Blender:
Blend File: para.blend (434 KB)
Just rotate bone “crank-1” to operate it.
Try to make your IK chains connected, not with gaps everywhere - put the bone connections at the centre of rotation of the joint, also your chain lengths for the arms are different, not good practice! The “Root” bone should be on the floor between the feet, or tracks in your case, parent major bones and IK targets to them. Don’t have limb bones floating in mid air - connect them to the major “spine” type bones - makes for a much easier life.
DON’T Scale or rotate object meshes, or armatures for that matter in Object Mode!!! That is what Edit mode is for, do all edits in Edit mode: :ba:
Just one example of many - if you must scale/rotate in object mode Apply the scale/rotation afterwards by keying CTRL+A => “Rotation and Scale”.
I am sure others will help you in my absence, if not I will be back early Feb. I would advise you read the manual for IK chains and look at Nathan Vegdahl’s “Humane Rigging” tutorials to get a good start in rigging.