The quadrupole orderings and lattice effects in 4f-electron systems with orbital degeneracy in rare earth compounds have been investigated by ultrasonic and thermal expansion measurements. A ferroquadrupole (FQ) O-xy-type ordering associated with a trigonal distortion in HoB6 with a Gamma(5) ground state is presented. The trigonal distortion in ordered phase IV CexLa1-xB6 (x = 0.75 and 0.70) with a Gamma(8) ground state indicates O-xy-type FQ ordering in phase IV. In both systems, HoB6 and CexLa1-xB6, C-44 anomalies are observed. In tetragonal HoB2C2, an ordered phase IV appears near a tetra-critical point, where the antiferroquadrupole phase II and antiferromagnetic phase III compete with each other. Noticeable ultrasonic attenuation and softening of elastic constants in phase IV of HoB2C2 due to quadrupole fluctuation with a slow relaxation time tau similar to 7 x 10(-9) s are found.