My GB maroons are about 4" and 2.5" and live in 4 anemones (2 green BT and 2 sebae)... The anemone's sizes range from ~12" diameter to 5" diameter and all are doing well.
flanders it really depends on the size pf the fish that are hosting the anemone and how often the fish are in the anemone. IMO & through my experince the fish ( both of them ) should be able to fit in the anemone with room to grow.