What should i do?

I found baby bird ( im guessing its a great tit).
I waited if the mother bird would have came there but i think they have been taken out of the nest n moved there. The bird dosent have the eyes oen yet so im guessing its under 4days (?).
2was already dead n one more died when i was waiting the mother bird.
I have now took the last one inside my home, made a small “nest” and kept it warm. Its bit more alive at this moment than when i found it.
The nights here where i live (Finland) are still cold, +11 celsius and raining most of the nights. We don’t really have places to bring baby birds like that specially at Saturday night.