Catalyzes the hydrolysis of fructose 1,6-bisphosphate (Fru 1,6-P2) and sedoheptulose 1,7-bisphosphate (Sed 1,7-P2) to fructose 6-phosphate and sedoheptulose 7-phosphate, respectively. beta-D-fructose 1,6-bisphosphate + H2O = beta-D-fructose 6-phosphate + phosphate D-sedoheptulose 1,7-bisphosphate + H2O = D-sedoheptulose 7-phosphate + phosphate Carbohydrate biosynthesis; Calvin cycle. Homotetramer. Belongs to the FBPase class 2 family.