Is it permissible to suffice with a simple, legitimate marriage contract (aqd shar'i) at the bride's home, in the presence of both families, to avoid forbidden acts and mixing (of genders), especially if the groom's family does not adhere to Islamic guidelines in large wedding celebrations?

If you know or strongly believe that there will be objectionable acts in a large celebration, such as free mixing of genders and musical instruments, it is obligatory for you to avoid it and to keep your family away from it. A small celebration is sufficient for announcement and publicity, and it is recommended that it be accompanied by the beating of the duff (a type of drum), and a walima (wedding feast) even if it is with only one sheep. If you combine all of this and avoid objectionable acts, then you have followed the Sunnah.