To give some context to the quote below, the scene concerns three people lost in the Amazon worrying that the monkeys in the trees are losing their fear of humans.

มันคงเห็นเราเป็นส่วนหนึ่งของที่นี่ไปแล้ว

"They probably see us as part of this place already."

1. Is ไป linked to เห็น in this instance giving a sense of direction to the verb , and if is is,

2. Could เห็น be interpreted as 'to regard as' eg

"They probably regard us as part of this place already"

In this interpretation would เข้า replace ไป in the sense of 'it has entered their minds'?

To give some context to the quote below, the scene concerns three people lost in the Amazon worrying that the monkeys in the trees are losing their fear of humans.

มันคงเห็นเราเป็นส่วนหนึ่งของที่นี่ไปแล้ว

"They probably see us as part of this place already."

1. Is ไป linked to เห็น in this instance giving a sense of direction to the verb , and if is is,

2. Could เห็น be interpreted as 'to regard as' eg

"They probably regard us as part of this place already"

In this interpretation would เข้า replace ไป in the sense of 'it has entered their minds'?

First of all, this set of words is not called คำสร้อย. They are serial verbs which are used for modifying initial verb to indicate the direction of motion or aspect of initial verb.

As for your questions,

1. ไป is not linked to เห็น, it's linked to เป็น. So, it has an aspectual meaning not directional meaning.

2. Yes, เห็น can be interpreted as 'to regard as' in this context.

In this context, เข้า can not replace ไป, because it's not link to เห็น as explained above.

I was also taught that ไป, มา (and to a lesser extent เข้า) are modifying verbs used to show direction in motion or whether the action is coming to or going away from the speaker, the subject of the sentence or the object being discussed. The very simple example my teacher gave is the two signs at the airport for arrival; มาถึง and departure; ไปถึง. She also used the example of in incoming call; โทรมา, and an outgoing call; โทรไป, even using the example of a return call; โทรกลับ to show the action goes both ways, out and back.

This is further illustrated in the often used thai sentence construct of having gone somewhere and just returned by using; ไป-place-มา like; ไปโรงพยาบาลมา

Sometimes I find it tough to discern which verb in sentences the "directional modifier" actually is modifying, as thais just stack their verbs in time sequential order with no linking words, but I'm getting better.