For the smaller squares ... do not cut them into triangles til after you have sewn them on.
Plus oversize them, so when they flip out and are pressed, you will have excess to trim off and can be sure the snowballed block is nice and square.
The challenge you will have ... the corners cut off the large block, were they cut to precision or not? If not, when you assemble all the snowball blocks the points will not line up.
You have some lovely fabrics ... I hope you can get it all to come together!
Good Luck!