I’m not really a fan of separate pieces that have to be joined together at the end. I like the option of crocheting the blanket in one piece better. If you take a look at the “risky” yarns beforehand and make a gauge swatch with them, which you also wash, then you’ll see whether the yarn shrinks. But only real wool shrinks if you wash it too hot.
I would also recommend using different crochet hook sizes: the thinner yarns with the larger hook, the thicker yarns with the smaller hook, so that everything evens out in the end. Every now and then you’ll need to measure the row to see whether everything is roughly the same width. At the end, you add a border around the blanket, which also helps hold it together.
I think the different qualities and thicknesses actually create a unique effect. Look, I once knitted scarves sideways. Lots of different qualities simply knitted together one after another.
Best wishes, Ina