It depends on which stitch you plan to use to stitch the appliqués down with. A buttonhole stitch should be fine without stabilizer. Straight stitch 1/8 in on the edge of the appliqués will be fine too. A tiny open zig zag will also be fine but a dense satin stitch may cause tunnelling without stabilizer. “ Tunnelling” is when the satin stitch bumps up to form a tunnel and it distorts and wrinkles the background fabric.