If theyr'e in parallel, then they'll just recharge from the other pack whenever current isn't flowing out of it.
Even if that never happens, then they'll still both be discharging, just at different rates.
As the lower resistance pack (which won't have as much voltage drop under the same load) drains, and it's no-load voltage drops to the point where it matches the higher-resistance pack's under load, then both packs will be discharging. A bit like a continously-changing leapfrog.
Exactly how it works out depends on each pack's cells' discharge curve and the loads on them, as well as the actual pack capacity.
Similarly, charging them in parallel also depends on their charge curve, and the charger's capabilities.
As for what internal resistance each cell has, you'd need to look at that specific cells' curves for that from the manufacturer. Every cell with the same capacity does not have the same curves.
There's a lot of threads discussing paralling various chemistries and pack sizes, whcih discuss what happens in various situations. Unfortunately no single search will turn htem up, but most f them are in the battery subsection, so if you look thru the thread topic list there, you'll find most of them obvious by title. Maybe a search in that section for just threads with "parallel*" in the topic would show you many of them.
You'll find that most things have been discussed here on ES if you poke around, and you can answer your own questions without waiting for someone to come along, if you need a quicker answer.