بسم الله الرحمن الرحيم
(1) Mahr Fatmi is 131 tola and 3 masha silver (1 tola = 12 masha). At present, it is nearly equal to 1600 gram silver. If you want to give necklace of 1 lakh value in mahr then you may do so.
(2) The feast arranged by bride’s family on the occasion of nikah is not sunnah, but it is lawful without any doubt. When the nikah of Hadhrat Umm Habibah (may Allah be pleased with her) was solemnized with the Holy Prophet Muhammad (may peace and blessings of Allah be upon him), the Najashi king who was intermediate arranged a feast on behalf of Hadhrat Umm Habibah (may Allah be pleased with her). This Hadith proves that the bride side can arrange feast.
So, it is not correct what you said to your in-laws that they may arrange the feast but you do not want to let your family members participate in it.
(3) The feast arranged by the boy’s family after nikah is called walimah. Similarly, If it is done the next day after the husband meets his wife, it is also walimah. And if one meets his wife immediately after nikah and arranges the feast it is also walimah. The best of walimah is to spend the night with wife and invite people for a feast the next day. Whatsoever is fed before nikah is not walimah.
Allah knows Best!
Darul Uloom Deoband