Hi Ann, you did not mention if you are 2 adults and 2 kids or 4 adults. If your kids are OK with sharing a bed then its not too bad to find a sobe to meet your needs. If you need 3 beds then it may be a bit harder to find or it may be easier to just rent 2 smaller rooms and be separated. If you have kids it was perfectly safe for them to have their own room in the RS recommmended places we stayed.
In Dubrovnik I highly recommend Sobe Renata. It was the best room with a view we ever had. The triple room was the highest place in town overlooking the harbor with a kitchen, 2 beds, low ceiling, and lots of room to spread out. Best deal ever at 75 Euros
In Korcula we stayed at Sobe Tedeschi on the top floor (Triple room) which had 2 large beds in a room and then a separate room with couch and kitchen table and kitchen. Also had a good view of the harbor and walkway. It was 90 Euro a night with breakfast. The owners were great and invited us into their home for wine and cheese and good conversation about the history of the area.
In Split we stayed at BASE sobe (the offsite apt) and it had two floors with bed on main floor and a bed upstairs. Plenty of room for 90 Euros with a kitchen. Just has low upstairs ceiling and a nearly vertical staircase but lots of fun for kids.
The above 3 places advertised a triple room but if you have two kids (<15 yo) that can share a bed then they could easily handle the 4 of you. If you like ambiance and location with good hosts I recommend these places.