that is the cutest panel where did you find it?

You could "float" some of the panel pictures in a wide border randomly and then add a plain black or black and white stripe "cut sideways" final border.
Use the smaller blocks in one quilt and the larger blocks in the other quilt, varying the borders to fit. Such a cute panel and so bright.

I like this idea except rather than buying new fabric, I'd use the pink and black with dots that you already have. I also like the idea of using part or all of the panels for pillowcases too.

If you back them with fleece (in different colors) you can add borders till the width is about 55 inches, whatever length and then sandwich with fleece. No inner lining is needed, fleece quilts beautifully, washable, comfortable, warm, etc. Binding would be whatever you have left from the borders, OR, piece the border fabrics and make the binding out of all of the fabrics.

They are adorable and will be well loved,

I would use some of the smaller blocks from the panel as cornerstones in the next border.

What about a very small print or check border of pink and red?

Beautiful quilts. I would bring in a bit of red.

I also think this is a great idea. Doing this will make them look at least somewhat different. And yes, do pillow cases with any/all of the fabrics. Use the Missouri Quilt Co. tutorial for those. I am making two each month for my grandsons to celebrate whatever is going on for that month ... Halloween, Christmas, Valentines Day, Birthday, etc. By the end of twelve months, they will each have twelve or thirteen pillowcases to choose from. Since I don't live near them, this is my way of staying in touch.

Adorable the way they are, maybe put different backs on them so they know who's who. Also name tag-with to and from, date information.

They're very nice so far! I'd vary the additional borders and backing as has been suggested so each girl will recognize her own quilt. And I think the suggestion to use the remaining panels in pillowcases is a great idea! Please post pictures when you're done!