For twins I might use the same fabrics but different patterns. You really could do just about anything but I wouldn't make them identical. My reason is I get bored doing the same thing twice but also they would be more personal to each child.

I made quilts for my twin great-nephews for their 1st birthday last year. In fact, these were my very first quilts. I, too, used Yellow Brick Road pattern because it was simple, and I knew I was doing two. My niece and her husband are both graduates of University of Michigan so I used a variety of UM prints and Detroit teams (Tigers, Pistons, Lions, and Red Wings) and bordered one in navy and the other in the yellow so as they would be a little distinction. My backing was a print of sports balls. I hope this helps.
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My massage gal had her 1st baby boy and we made this quilt for her in aqua and yellow. She loved it so much she wanted the same pattern made for when she had her twin boys a couple years later using the same aqua but wanted one with green added and the other one made with orange. Then she thought how would she decide which one to give to which boy so she asked if I could just include both colors with the aqua. I thought I'd make up a block and see how they looked. Took it to her and she said.....YES. So both boys got the same quilt and there's no fuss from either one of them. Here are the quilts I made for the 3 boys. For all 3 quilts I used the cut-offs from the blocks to add to the borders and then again for the backside. Love when I can use up all the scraps and cut-offs on a quilt.

a coworker that I loved had twin boys so I did a Batman quilt and a Superman quilt. She loved them and the boys used them until they fell apart. Last year a dear friend had twin girls and I did a Wonder Woman quilt and a Supergirl quilt. so much fun!

Make the same quilt just put there names on them that is if the mother dresses them the same.
If she doesn't make them different.

I have boy/girl twins. Personally, I would make something totally different. I would make a Train/car quilt for one child and a tractor/farm quilt for the other child.....maybe using the same fabrics. This will buy a good number of years for each child.
Guess I march to the beat of a different drum.

My friend had twin boys I used Dr Suess fabric Thing 1 and Thing 2 mixed with other Dr Suess fabric

I knew some girl twins growing up, and they did not always like everything the same. Are you planning to put their names on them? There will be no mistaking who owns which.

As to patterns, there are many that would be great. I like Warm Wishes or Boxed Squares.

I like Warm Wishes with different little boy fabrics. I am finishing 1 for a little girl & found you do need to watch the placement on the rail fence blocks because they frame the focus fabric different.[ATTACH=CONFIG]611044[/ATTACH][ATTACH=CONFIG]611045[/ATTACH]. I did fine with the rows but got the rows mixed & had to rip & resew.

My Mum is an Identical twin. If I were to ask her she would say make them two completely different quilts. They are unique individuals and should be treated as such.