One of them sadly died one day in morning, and the day before his death, at night he was not moving much, putting his head down on the stone and his legs/hands fully out (imagine yourself lying on bed with hands and legs spread motionless). I thought he was just relaxing so i wasnt worried, but later (the next day) he died.
Now i have one more baby 4 month old RES who was lying just like my old (dead) turtle

I am very vorried that he might die too! I couldn't get a proper pic of him lying like that (with his head fully out and limbs out and everything motionless and very lazy) as now he is swimming a bit.
Please give me some advice on what i should do!
thanks!
p.s. = i will be attaching some recent pics of him too, (before he started ating odd)
the one with less white patches is 'bolt' i.e. the turtle in question.
https://ibb.co/0M42ss9
https://ibb.co/F4nphW8
https://ibb.co/RHXGJnj
https://ibb.co/9NW1Dbv