No sign of IPs, sells couple of thousands per month, and no issues visible on the listings.
However brand has mentioned not to sell it’s products online/marketplaces on the brand website but obviously sellers are selling.
What do you guys suggest?
I would personally avoid those listings if the brand explicitly states on its website that its products cannot be sold on Amazon or other marketplaces. The fact that several sellers are currently doing it without visible IP complaints does not mean the brand approves of them or will not enforce its policy later.
You could invest heavily in inventory and then receive a complaint, lose selling eligibility, or simply be cut off from the supply chain. Amazon generally allows legitimate products to be offered by multiple sellers, but that does not override contractual or distribution restrictions imposed by the brand.
For wholesale, I would rather find brands that explicitly authorize Amazon resale and can provide invoices and, ideally, written authorization. The sales opportunity may look attractive, but the additional risk is usually not worth it.