Help please!, eo

Hello,
Can someboy tell me please what ( eo, quod non aliunde eo immigrassent nec patriam sedem mutassent umquam) means? what does the first eo means? and the second one is an adverb? I understand the context but I can not find the function of each word in the sentence. which form has immigressent? it means immigrant, doesn’t it? it derivates from immigro? which structure is it? with best regards

Antisthenes ridere solebat Athenienses iterum atque iterum gloriantes, quod essent αὐτόχθονες [autochthones] – hoc est indigenae – eo, quod non aliunde eo immigrassent nec patriam sedem mutassent umquam

The first eō is the ablative, neuter, singular of is. The following quod refers to it. Basically, you can translate eō, quod as for the reason that. The second eō is an adverb = in eum locum.

immigrāssent = immigrāvissent

Maybe you can give it another try now.

Thanks so much!