they just need some place to purch on comforatably without much struggle.
They also need an easy way to there perch. If the water levle is only about 5 inches then I would not worry about them struggleing to get to there landing spot. However if the water levle is any hire then u must supply a laddder of somesort. Red claws can swim about 6 inches off the bottom .You can also buy a turtle platform that sticks on to side of the glass. That would provide plenty of space for them. Since it is only a five gallon I would recomend u cut the platform as they can be kind of large.
Since it is only a 5 gallon I would recomend u only put 1 - 3 in it. Red claws are territorial. Also u must have several hidding places for them to molt, as they are very vunerable when they molt.
They might try and make a grab for your guppys but, I doubt they will ever manage to ketch them. Unless they are sick or something.