4 nights in Seville - Enough?

I'd probably go for three nights in Granada. That would give you one full day for the Alhambra plus another full day for the many other sites there. Three nights in Seville are plenty. I really like the Alcazar and Cathedral, plus the surrounding quarter. IMO those are the only must sees. I'd also add a Flamenco performance one evening. Plaza Espana is a nice area to walk, but really not historic or particularly special. The Golden Tower is also nice, you can either walk buy or visit the museum inside, either way it won't take too long. You may also want to attend a bullfight one evening (if they're running). We went, and are glad we did, but it's not necessarily for everyone. There are also Roman ruins not far from Seville that may interest you, but require transportation. A half-day in Cordoba would be nice to see the Mesquita and surrounding quarter. I'd try to get there if you can make it work.

I am also going to Seville for three nights....do you think a day trip to Rhonda is in order?

It's all opinion, but I'd stick with 2 nights in Granada and 4 in Sevilla. I personally found Sevilla to be a much more interesting city than Granada. Plus from Sevilla, you can easily take a daytrip to Cordoba, which I highly recommend. The Mezquita is unlike anything else you will see and the old quarter is great to just explore. You could also do several other daytrips from Sevilla, including Roman ruins and the hill towns.

Susan, From Seville, Ronda is about a two-hour drive. It's a doable day-trip but includes four+ hours of driving, so likely to be a long day. A bus might be a good, inexpensive way to get there without having to drive, but you would have to check the bus schedules to see if they work there and back. We visited Ronda and enjoyed it, but did it as a stop along our route and spent a night there.

Susan, From Seville, Ronda is about a two-hour drive. It's a doable day-trip but includes four+ hours of driving, so likely to be a long day. A bus might be a good, inexpensive way to get there without having to drive, but you would have to check the bus schedules to see if they work there and back. We visited Ronda and enjoyed it, but did it as a stop along our route and spent a night there.

Susan, From Seville, Ronda is about a two-hour drive. It's a doable day-trip but includes four+ hours of driving, so likely to be a long day. A bus might be a good, inexpensive way to get there without having to drive, but you would have to check the bus schedules to see if they work there and back. We visited Ronda and enjoyed it, but did it as a stop along our route and spent a night there.

Your plan sounds good, especially going to Cordoba to see the Mosque. It's an absolute must.

I have been to Sevilla 2 times, once for 2 nights, the second time for 3 nights. Three nights is perfect for Sevilla to take it all in at a relaxed pace. Make sure you book a flamenco show. You have 4 nights so yes, day trip away.
When in Granada, make sure you bring a swim suit and go to the Hamman Arab bath house. Three pools, all at different temps, relaxing as can be, sipping on some mint tea. It was wonderful and maybe the highlight of our trip to Granada.