Meaning of 見て取れぬでもない and 揃って

Question

I'm trying to understand the grammar behind this sentences:

親子関係に見て取れぬでもないその二人は、トーマス井口が店の中に入ってきた途端に揃ってガッと目を剥き、信来の客の容貌をしげしげと観察し出した

I think I got the gist of it: The two people inside the store looked like they were parent and son, and as soon as Thomas Iguchi walked in they looked fixedly at him, observing him.

There are, though, two places I'm guessing:

1) 見て取れぬでもない: I found that 見て取る means "to perceive; to grasp (the situation)"; 見て取れぬ sounds negative, so with the following negation I guess it's again affirmative, でも maybe is the "things like" でも, and れ comes from a potential form, so "they could be perceived as parent and child"? I think I can guess the general meaning, but I have no clue why such a declination.

2) 揃って: as far as I know it means "To be completed; To be satisfied (of conditions); To be equal; To assemble" and similar things; but I can't really make sense of it in 入ってきた途端に揃って: 入る ("to enter") + 切る (I guess it gives a nuance of Thomas having fully entered in the store) + 途端 ("as soon as") + に揃って (no idea). Does it means something like, after entering Thomas is gathered in the store with those two people?

Edit: On a second thought, れ in 見て取れ should be a potential form, it doesn't fit the passive declination.

Edit: While looking into this I found that 揃って is a form per se, meaning "all together"; could it mean they are in the store together? Or the two people looked together at Thomas? I'm kinda at a loss.

Answer 1

1) Yes, you're correct. 見て取れる is used here as the potential form of 見て取る. 見て取れぬ is just the negation and でもない negates it again. I think it is something like "It is not that they could not be perceived as parent and child" if you want to be literal. This is more commonly used like ~ないでもない and generally indicates that one isn't super confident in what they are saying or only somewhat feels that it is true.

Here are some examples from A Dictionary of Advanced Japanese Grammar:

あなたの苦しい気持ちが分からないでもない I do somewhat understand the pain you are feeling.

あの時大学を辞めたことを、今では少し早まったなと思わないでもない Now I rather feel that leaving the university at that time was a bit too hasty.

そういえば、そういう話、どこかで聞いたことがあるような気がしないでもないです Come to think of it, I seem to feel that I've heard something like that somewhere.

2) I think it's used here to say that the two people looked at Iguchi together in sync. Like in the same way/at the same time kind of meaning. I'm imagining Iguchi enters the store and the people in the shop suddenly look at him like this (well maybe with a more suspicious look in their eyes):