Re: Bath time
Ours like to play in the tub/shower, too. They especially love golf balls (too noisy), golf-whiffle or solid plastic balls (still sort of noisy) and crinkled paper (not noisy at all, just a lot of crinkling and thundering feet echoing on the tub).
Marmy used to LOVE to hide in the hall bathroom's tub. He'd ..j..u..s..t.. ..b..a..r..e..l..y.. peek his dilated eyes and flattened ears over the edge and then spring out at you sideways, tail fuzzed-out like a Wild Man with a little "mer-rowr!" cry.
Ours wouldn't play with *other* cats in the tub, unless it was a herd of foster kittens, the adults would only entertain themselves in there. I think they loved the noise. Your three look like they're having fun.