Elizabeth, the crucial info is here:
* I'm interested in learning what to do with cash
* I'm 71, husband is 69, so conserving principle is primary.
* Have 55% in stocks like Berkshire and company.

You have most of it worked out, and very important to see the forest rather than the trees here - one might frame the situation as follows: Berkshire is providing the tailwind of value, and you are then wanting invest cash in a way to get (1) the best return (2) without capital loss.

Most of your capital is having the value accumulate in Berkshire - I write 'value' in contrast to the 'quote' which can fluctuate wildly - the value will go up fairly consistently somewhere in the 4%-12% range almost every year. Perhaps you are drawing income from the your cash equivalent part of your savings, in which the larger change in Berkshire quotes don't matter.

For the cash component of your savings, the main insight I could offer is to focus on [2] above (preservation of those savings), and not worry about [1] (the return) so much.

With both bonds and cash equivalents you will not get a good return anyway, no matter what is done. As the yield grows beyond the 10-year bond (presently yielding 3.5%) then you are likely introducing a risk of not having the savings returned at the end of the term.

Getting an extra 2% on your cash/bonds part of your savings is not going to make any noticeable difference to you or anyone around you, but losing all of it would make a difference - so I would treat the cash mainly as preservation of capital, and then enjoy the value accumulation of your 55% of savings within Berkshire.

>Is it wise to keep my accounts at Schwab or move them to Fidelity and Vanguard?

Vanguard has a good reputation, but I doubt it it matters much where the accounts are (?). I presume that they all operate under the same US regulations, so perhaps simply investigate the comparison based on their costs, and move your account where the cost is lower.

- Manlobbi