You think you may have a shower pan leak. So non sanded grout is employed most often. If you just seal with silicone, make very sure the area is dry and work in plenty of silicone.
You can merely remove and replace the damaged caulks around the tub. https://Parentingliteracy.com/wiki/index.php/How_To_Create_Ceramic_Tile_The_Cheap_And_Easy_Way