Can you swim there?

Yes

You can walk the river between first and second falls, with few deep pools here and there. And yes after 4th fall there is a nice big, deep pool but hike there is extremely difficult though short. Also you can take a shower under 3rd fall.

I have many times, beautiful area.

The top/first waterfall has a deep pool, ive seen people swim there, then at the base of the 4th fall there is an accessible pool but the later is an intense hike although only a short distance of probably less than a mile. The last fall i would not recommend for children under teenagers.