Is Lupinrangers sent a wrong message to kids and teens?

Not exactly. But, I do like the idea that the gentleman thief sentai are acting like a true sentai as opposed to the secondary police-themed sentai, so far.

Well, kaitou fiction is an entire genre in Japan and a lot of that includes media aimed at kids. Typically in kaitou shows the justification for the characters' actions is "s/he may be bad but the villains are worse!" so Lupinranger Vs Patranger is, if anything, more child-friendly with the idea that the Lupinrangers only steal to help save people they love (and they only ever steal the Lupin Collection)

The Lupinrangers are ultimately on the side of good, it's just their message is "The ends justify the means" in contrast to the Patranger's "The means justify the ends", so no they aren't bad role models are anything, they just have a different way of doing things.

As several said in their post (mainly Kaizoku Blue), LupinRanger vs PatRanger is pretty much based in Kaitou, a genre based in Arsene Lupin series, but also in Lupin III, the Monkey Punch character, which is (arguably) a teen manga (in fact Keiichiro is closer in personality to the cop Zenigata, at the beginning), which is very popular in Japan, that excelled the boundaries of its own genre and marketed audience. There was mangas, sequels, several animes, spin-off, all popular with young people and adults (and films, even one directed by Hayao Miyazaki). Even the Persona 5 character (like a lot of people said) is based in the Arsene Lupin's novels.
The genre is very popular, not only with teens, also with boys. It "romantizaced" the idea of thieves whom steal to bad people, and in the end they helps people. Think it like Robin Hood for Western audiences: he steals the rich ones to give it to the poor one. Also american superheroes, which in most the times are vigilantes (outside the law) with secret identities.

Hmmm, that's a difficult question. I doubt parental guidance would be effective here due to how morally grey the Lupinrangers are and no parent wants to tell their kid that stealing is okay. It's probably better for younger viewers to learn by watching the conflict and considering both sides' motivations. LupinPatren is already doing a great job showing how each side has good and bad points. I think if this were just Kaito Sentai Lupinranger without cop co-protagonists then there'd definitely be a problem with the lack of lawful good characters to remind viewers that stealing is wrong, regardless of motivation. Which is why the VS theme is necessary for this cops and robbers show. Imagine Gokaiger without legendary Sentai or Kyuranger without Jark Matter. Eventually, you might start to question why these Sentai are heroes, what makes them good guys? Under what circumstances does stealing suddenly become acceptable? Law and chaos are like LupinPatren's yin and yang paradigm, they're both important but you can't really understand half without seeing the other and what makes them different.