Can the recipients in a will/living trust be changed without seeing a lawyer?

Generally, a will can't be challenged before the death of the person whose will it is. And even after, you might not have standing to challenge it.

Yes, he is alive and he sent me a copy of the changes.

Holographic wills are legal in California according to the California Probate Code Section 6111. There are requirements in the case of holographic changes. This is a legal matter, but in short, yes, if correctly done, this is legal. If you are a beneficiary or have other concerns you should consult an expert--a probate attorney--to answer this question.

It appears that in California, a will can be amended by creating a "codicil"; this needs to be witnessed but it doesn't need to be notarized.

I'm curious. Is your BIL still alive? If he is, how do you know that he changed the beneficiaries?