ok so yesterday i brought from the forest 3 young oak trees they are around 24 cm high (one is only 11 cm high and all of them are 3 mm thick), now my question is do i keep them inside during the winter so they dont lose leaves and continue expanding or do i let them lose leaves and have their overwintering period (i am asking this because i am not sure they will survive winter outside)

No dilemma there; It depends on the oak species.. Are you talking Quercus Robur / Petrea? Pop them in the ground and leave them there for winter. Don't try to keep there indoors. They will most likely not survive winter indoors; Light levels are too low, there is not enough air movement. The air is too dry. The tree needs winterrest etcetcetc.

Is it cork oak, stone oak etc (Mediteranean species): Keep them in a shed, sheltered from wind & frost, or in a very cold bedroom (<10-15 degrees celcius)

how low can the temperatures drop before i have to move the trees to a more warmer place and btw her are some pics of oaks

They seem like pretty standard oaks to me; Would not worry to much about finding a spot. These are very hardy buggers. Once they shed their leaves, thake them out of the direct wind and in a corner of your balcony. (Better would be to bury the pot in the garden). Wouldn't lose a night sleep over leaving them in a sheltered spot outside the whole winter

If they're your average oaks, and I'm assuming they are, then they love being outdoors.

Considering you got them from outside I dont see how they wouldn't do well over the winter. They're obviously native to your region.