Another idea is blocks with meaningful names. If he played cards a lot, there is Card Trick, for example. If he loved mountains, there's Delectable Mountains Etc.

If he liked reading, you could make a block with a bookshelf and embroider the names of favorite books.

AND
There is no reason why you can't mix all the different ideas in one quilt!

I like what Karen and Wendy made and said! But, since you are to make 3, you might want to simplify it a bit. If you can work some of his shirts along with printed fabrics (in place of transferred photographs) with his interests, that could speed things along. If you have the knowledge and time, photos are wonderful. If not, maybe just do one, and then add football, basketball, racing, pets (or whatever) fabrics in workable sizes.

Dawn

I'm not sure how old her son was so maybe a younger guy wouldn't have as many woven cotton shirts as a man, but when my friend's husband died I made her a quilt from his shirts.
thequiltshow.com/community/kfstitcher/photos/photo?albumid=10108522&photoid=114640
I used the leftovers to make a quick lap quilt for their son.
thequiltshow.com/community/kfstitcher/photos/photo?albumid=10108522&photoid=114639
If he wore more t shirts perhaps you could make them memory t shirt quilts. There are books to help you get started on one of those.
Good luck. It's nice of you to take on this project that I'm sure will mean so much to them!

What a lovely idea but a lot of pressure for you. To begin with I'd look for photos to transfer onto fabric of her son with them, family and friends. Then what were his interests and hobbies and they could be represented by applique or fabric featuring them and same with pets and maybe food. You could include places he liked or holidayed at that were significant.
Another thing you could do is use his clothes to incorporate in the quilt.
I think I'd do a lap size quilt that his mum can snuggle into when times are hard. The design depends on the elements you want to include. Square blocks for each topic would work or you could do an applique tree with a memory in each leaf and names of family on the branches. Here's a link to some ideas on pinterest link

It'll be really emotional making this and I'd probably stick to the one using his shirts and just squares of the fabric. Lovely thing to do for her, you're a true friend.

a friend of mine lost her only son just recently and I said I could make her a memory quilt for her. She has asked me to make 3 memory quilts for her , her grandson and the daugher - in-law. All good , but I have never made one before. Has anyone made one and maybe you can give me a few clues on how to tackle it ? Cos I think I have bitten off more than I can chew here.