Just use sealed AGM batteries, don't burn your house down or deal with spilling chemicals everywhere.
Even just drawing in parallel from batteries like this is a fire hazard. Charging is an out of your mind goal.
I think you've confused parallel with series; in parallel, the batteries will naturally balance themselves to the same voltage and discharge proportionally to their capacity. It's the series configurations that are riskier and need extra balancing circuitry.
Also, I'm pretty sure the bulk of fires are from the much more fragile pouch "lipo" cells, not hard-cased 18650s like these. You may note the extremely large number of lipo fire videos on YouTube as evidence.
On the other hand, 18650s tend to be quite a lot more robust and difficult to ignite:
If you're building a large pack you don't want cells with a built-in protection. You connect all the cells to a pack-wide BMS that keeps things safe.
The important thing is to never use unprotected cells without some protection circuit in the pack.
I'd not have known how much of a bad idea this was had I not been a long time fan of EEVBlog. It's an entirely different world when touching Lithium cells. Even drawing in parallel from cells from the same batch can be a bad idea.