Hmmn....they are giving me Impel Down beast vibes (albeit a lot more menacing) and although their silhouettes look pretty terrifying they don't look very bright tbf and Queen's comments this chapter seem to imply that. So my guess is that they are Ancient Zoans that have gone through forced awakenings.
With regards to how strong they are, my guess is that they are all mid tiers with Numbers 9 (I counted 8 in total) being the strongest, so a high mid tier and Numbers 2 being the weakest, so a low mid tier. I mean going off the card theme Kaidou's crew is based off of, they should fall right under the calamities, so I reckon mid tier is just about right. So yh, I reckon they are comparable to the flying six. That said I don't think their stats will be identical. This is still just my personal take on it but I reckon the Flying Six will have more balanced stats overall where as the Numbers would have skewed stats in stuff like strength/durability for example (i.e. they'd have filthy strength & durability/endurance stats to compensate for what they lack for in intelligence etc.).
Lastly, considering the Numbers fall in line with the cards in a card deck like the calamities, it could be that these dudes were Kaidou's original crew mates and the guys like the Flying Six and the Headliners are newer additions which is why they are based of card games. I mean Kaidou has been actively recruiting strong fighters for the war he wants to start so it makes sense that the strength of his crew isn't directly proportional to other Yonkou crews (for example, having so many mid tiers in comparison to Lilin's crew for example)