Hello Evaldas, I would wait two more weeks on the large pup and maybe a month on the smaller one. When you decide to remove the pup take a shovel and make and sharp strike (smooth cut) to the dirt between the pup and the mother keeping the strike closer to the mother to assure you obtain some root structure for the pup. But not to worry bananas are as tough as nails. No need to place it in a bag that will do more harm than good. When bananas are small and being grown in pots they prefer to be in partial sun (to prevent steaming the new roots) and prefer the soil to dry slightly (lots of perelite in the soil mixture miracle grow potting soil will do well) between waterings this will insure soil borne disease dont take hold, once the are larger (2' or more) they like the exact oposite of that; lots of water and full sun. My wife and I cultivate bananas and are currently growing around 30,000 bananas/25 species. If you have any questions feel free to ask we will help all we can. What zone are you in? if you are in zone 7 or below you can place the plants in 3/4 sun or above. for this process. Best wishes Shawn and Angela, Florida hill nursery.

Thanks for the info :).
I'm in zone 5.
What about using some rooting hormone?