They communicate with you directly
Let's clear up the underlying assumption. The flock of familiars spell is still cast by you. The relevant part of the find familiar's description says (emphasis mine):
Finally, when you cast a spell with a range of touch, your familiar can deliver the spell as if it had cast the spell. Your familiar must be within 100 feet of you, and it must use its reaction to deliver the spell when you cast it. If the spell requires an attack roll, you use your attack modifier for the roll.
Meaning the spell is still cast by you and so the additional familiars are yours. (This also means it only summons two of them [assuming cast at 2nd level] since you have a familiar already.)
So, because they are your familiars they can communicate telepathically with you (the Warlock), but they don't have to (and gain no ability to) do it via the preexisting familiar.
As they are summoned and communicate by you, their telepathy-range (of 1 mile) is counted from you, not your familiar even if you cast flock of familiars through your familiar.
In terms of senses they use the same rules as find familiar which includes using your action to perceive though the senses of one familiar, as long as that familiar is within 100 feet of you.
As more a side issue, there is some ambiguity as to what form the new (temporary) familiars can be. The flock spells says it can be any form of a find familiar familiar and Pact of the Chain reads:
When you cast [find familiar], you can choose one of the normal forms for your familiar or one of the following special forms: imp, pseudodragon, quasit, or sprite.
--- Player's Handbook, p. 107
As Pact of the Chain specifically refers to casting the spell and not just to "familiars you summon" it could be argued the new forms aren't available to the flock of familiars spell. I personally would rule otherwise1 and you should check with your DM which way they're going to rule.
An additional possible concern, you can cast flock of familiars through you familiar, but is unclear what effect it will have. Specifically, it has a range of touch, but does not refer to the target of the spell at any point. It also doesn't clarify where the familiars appear (such as "an unoccupied space within range"), so it is possible the intent is your familiars appear "from your touch", but it is not clear. If we assume (or rule) this, casting it though your familiar would let them appear at it, but have no effect beyond that.
1: On the simple basis that it is cooler that way (Rules as Fun) and that Pact of Chain doesn't account for multiple ways to gain familiars, because at time of printing there weren't any other than find familiar (Rules as Intended).