My mom had an antique quilt - made by my Gram back in the 30s...that was stored in the attic and some mice made it their home....so holes like the problem with yours. I fixed it by finding very similar fabrics ....then whether triangle(s) or square (s) - i made an applique patch in that shape - with enough to cover until i was into really good quilt fabric - applied the applique on the front - added batting where needed - and appliqued an adequate piece of white over the hole on the back. It was a bit of a long process - but it turned out very well and allowed the quilt to be gifted to my sister. GOOD LUCK !!