They may try and use Exodus 1:6 but actually the Bible doesn't help them. Genesis 50:22-26 says (emphasis mine):
22 And Joseph continued to dwell in Egypt, he and the household of his father, and Joseph lived for 110 years. 23 Joseph saw the third generation of E′phra·im’s sons, also the sons of Ma′chir, Ma·nas′seh’s son. They were born upon Joseph’s knees. 24 At length Joseph said to his brothers: “I am dying, but God will without fail turn his attention to you, and he will certainly bring you up out of this land to the land about which he swore to Abraham, to Isaac, and to Jacob.” 25 So Joseph made the sons of Israel swear, saying: “God will without fail turn his attention to you. You must take my bones up out of here.”26 And Joseph died at the age of 110, and they had him embalmed, and he was put in a coffin in Egypt.
So what do we see?
a) Joseph was still alive when people were living for much longer (the dwelling for 70-80 years hadn't kicked in apparantly) so the WT are making a comparison to a time when people lived longer.
b) Joseph saw the third generation of his son, Ephraim, son's. So that's actually 4 generations that overlap across a 110 year period. Not 1 generation made up two overlapping groups over 100 years...
The WT must hate the Bible when it doesn't support their fantasy doctrines.