I am in a mixed relationship, I'm white, and my fiance is Mexican.

My grandfather passed away from stage 4 cancer in 2019, and I am still struggling a bit with the grieving process. My fiance has offered and welcomed me to celebrate Días de los Muertos with him to help me cope, last year he got me a sugar skull and encouraged me to write a letter to my grandfather to put under it. This year is a little different, we can have an ofrenda for him, I just need a picture. My question is about the picture. Can I use a photo of him with my grandmother, even though my grandmother is still alive? Is that a bad omen, or taboo? It's the only physical picture I have of him, but I don't want to insult anyone with my ignorance or do something I'm not supposed to. I want to be able to celebrate this with him as respectfully as possible since he's letting me take part in his traditions, but I also am a little embarrassed to ask him some of the questions I have because I feel like they should be common knowledge, if that makes sense. I know it's many months away still but I'm packing to visit him at the end of the month and I'll be there during November when it happens, so I'd like to know if it's okay to pack the photo of my grandfather and grandma with me to use for Días de los Muertos. If anyone could clear this up for me, or offer some advice to help, I'd greatly appreciate it. I struggle with anxiety so I would be grateful for any insight, or tips from those who celebrate. I've done some research online, but I find it hasn't been as helpful and I'm worried I'll mess something up.

I'm also not quite sure where to post this, so I hope here is okay.