What a nice rememberance of your MIL. The blue & white do look like she had started a sampler quilt. I think I'd make a table topper with the 4 . Easy enough to add another color in too. You could also begin adding to each individual block- maybe adding yellow strips, to increase the size and then make a nice lap quilt.
The string blocks are easy & fun but to do something not a quilt I might use them for a couple of totes for grandkids. If there are young grand daughters maybe a doll quilt. I used a couple that size & made a sewing machine cover.
As for the purple one I too would enlarge it & make a lap quilt. I'd sit down at the drawing board & just draw out some rough ideas.
Best of luck & be sure to let us see what you do