Salaam all
Cleaning took longer than I hoped!!
I was raised surrounded by relatives into taveez. Luckily, my parents werent too keen on the practice so dont recall ever having to wear one. I find taveez a strange concept. It is supposedly there for protection, with the words of Quran. Yet our prophet Muhammad (pbuh) never commanded hanging verses be it in amulets around a person's neck, or cars etc as is common practice nowadays. Instead, the emphasis was always on reading Quran, recital and pondering and reflecting. That is where the most benefit is drawn from.
Just to clarify, it is general scholarly consensus, that taveez is not permissible to be used as protection. If however, say you have some Quranic verses hanging on your wall at home, such as ayat-ul-kursi, and it is there to remind you to read it and gain benefit from it, then that is allowed. If it is hanging on the wall as a means of protection, then that is not permissible.
As for khatams, I remember my great aunt saving thousands and thousands of stones from dates and using them to read ayahs from Quran or duas or durood during khatams. I remember i used to get sooooo tired but never dared say anything because I felt that would be a terrible thing to say!
I also remember when my great uncle passed away, there were rituals for doing khatams, on the 3rd day, the 11th day, the 40th day and so on. I can't remember how many of these rituals were observed, but at least 3rd and 40th were quite common. It is scary how far we come away from the true teachings of islam when we start going down the line of what we believe to be good instead of what Allah and His prophet (pbuh) prescribed to be good.
The following is taken from islam-qa.com.
The Prophet (peace and blessings of Allaah be upon him) said: "When a person dies, all his deeds come to an end except three: sadaqah jaariyah (ongoing charity, e.g. a waqf or endowment), beneficial knowledge (which he has left behind), or a righteous child who will pray for him." (Reported by al-Tirmidhi, no 1376; he said this is a saheeh hasan hadeeth)
Prayers for forgiveness offered by both sons and daughters of the deceased bring great benefits, as the Prophet (peace and blessings of Allaah be upon him) said: "A man’s status will be raised in Paradise and he will ask, ‘How did I get here?’ He will be told, ‘By your son’s du’aa’s (prayers) for forgiveness for you." (Reported by Ibn Maajah, no 3660; see also Saheeh al-Jaami’, 1617)
Another thing that may reach the deceased is sadaqah (charity) given on his behalf, because ‘Aa’ishah (may Allaah be pleased with her) reported that a man said to the Prophet (peace and blessings of Allaah be upon him): "My mother has passed away, and if she could have spoken, she would have given something in charity. Will she receive a reward if I give something on her behalf?" He said, "Yes." (Reported by al-Bukhaari, Fath, 1388)
Sa’d ibn ‘Ubaadah said: "I said: ‘O Messenger of Allaah, my mother has died. Should I give charity on her behalf?’ He said, ‘Yes.’ I asked, ‘What kind of charity is best?’ He said, ‘Providing water.’" (Reported by al-Nisaa’i)
Other deeds that may also benefit the deceased are Hajj and ‘Umrah on their behalf, after the living person has first performed Hajj and ‘Umrah on his or her own behalf.
lost sis, it can be very tricky challenging people on practices, especially if the occasion is quite an emotional one, such as death anniversary. If you feel you can, then bring it to the attention of your DH. If not, then just do the prescribed actions as stated above, make lots of dua for your FIL - he sounds like an amazing person mashallah, give charity on his behalf and ask Allah to show you a way.
My inlaws are very much into these practices too, I have been unable to change their ways, but I have told them very very gently and nicely that I cannot participate either. My situation was easier in that DH isnt into it either and much more strict than I am. Having said that, it has strained relationships a bit between him and his family too .
That is why my personal advice would be to start from your DH snd go gently. Let him take the lead, should he be willing wrt the family - I know from DH's experience that his family are so into taveez and khatams that despite showing them evidence of the bidahs, they have still clung to them
I do go on a bit....sorry.