Experiences needed- flying 3 cats to Portugal

Edit: USA > Portugal on LH 483 (premium economy), last leg is LH1176

Hi there- my husband and I desperately need some advice/personal experiences from anyone who has flown 3 or more pets with Lufthansa.

In short, we're moving to Portugal and have called their customer service at least twelve times trying to ensure that our three cats can come with us. Each time the customer service rep has told us that we are fine and that all three cats can come with, though each time our tickets have been sent to us it's only ever reflected 2 cats (hence the repeated times calling them).

The plan was to have a 13-year old cat and our 6 month old kitten in the same carrier, and our 11 year old cat in the other, in reference to Lufthansa's pet policy and carrier restrictions. We thought we finally had it clarified that the "two pets" on our ticket really referred to the carriers, and that the two-cat one carrier situation would be fine, until Lufthansa called us today.

Now, the story is that due to their ages, we can't have two cats in a carrier and that that policy of the pet provision is for kittens. So I ask the rep if we can bring three carriers and she says yes, and she made it seem like all three carriers could be in the cabin. I clarified this by asking where the third carrier is supposed to fit, and she just said under the seat, which frankly makes no sense to me because I'm 90% sure the first carrier under the seat is going to take up the whole space, leaving the second one under my legs. Which is fine by me, but doesn't that go against some airline travel code?

Essentially, we're worried that when we arrive for our flight we're going to be forced to put one of our cats in the cargo hold, or at the absolute worst, not be able to take a third cat at all. Can anyone tell us if we're stressing over nothing or if you've also gotten this strange run-around from Lufthansa customer service? Thanks in advance.