Two twist grain boundary phases (TGB-A and TGB-C*) have been observed in binary mixtures exhibiting a NAC multicritical point. The observed TGB phases are of very high thermal stability - for some concentrations the temperature range of their existence was as large as 40 K. Optical properties and textures has been investigated. Cane lines in the whole region of the TGB-A phase were observed. The pitch of the helix along with the rotation of polarization plane of light has been measured. A distinct influence of surface interactions on the stability of the twisted smectic A phase has been found.