Introducing new turtle into tank

Hello everyone,
I have a 3.5 inch YBS Charlie, recently I got a new baby from someone who couldn't keep it , it's a 1 inch res baby.... I have a 40 gallon tank for my Charlie and had the baby turtle for almost a week and in about another week or two want to put the baby in Charlie's tank..... My question is if I put the baby into my 40 gallon tank should I lower the water level ( I have my tank about 25 gallons full) ?? Also should I use a tank divider for the first month or Si since Charlie is a bit bigger that Sammy???

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My current set up and pic of Charlie basking and Sammy in my palm

I would fill the water up more. I have a 40 for my razor back musk that are 2 inches and it has 14 inches of water in it. Sliders loveeee to swim. You could put a divider in there to be safe. Sometime turtles arnt aggressive toward each other sometimes they are just depends. Maybe keep an eye on them..

Oh I know they love to swim my Charlie is probably the most active turtle ever lol my only concern is Sammy who is mate 3 weeks old at most I just want to make sure it can come up for air easy ....,.. And tank divider it will be ! I had put them both in a shoebox so they can meet each other prior to me adding Sammy to the tank and Charlie is scared of it he goes in his shell and runs away from the baby which I was surprised about because he's a very social turtle towards humans but I guess he just doesn't remember what other turtles are lol I had him since he was a hatchling as well

My razors were only a few weeks old. I put a lot of climbing spots and plants to climb up, before they crawled a lot to get air. Now they swim up. Maybe just watch them and raise the water over time

They are both so cute..

Adorable red sliders!

Thank you the older one is a yellow belly slider or cooter I was told different things by different people