Rabbits are little poo machines ! They should improve as they get older. Alot of people advise moving the litter tray to where they wee (if that is possible) & putting stray poos in the litter tray. You mention straw but do they have hay Milla? Rabbits should eat lots of hay which should be about 90% of their diet.
I love how dedicated you are to looking after your bunnies & learning how to care for them