No tax implications in the accounts, if you're selling and buying something substantially different. Going from individual stocks to mutual funds or ETFs is exactly that.
My MIL is 88, and she took over DFIL's IRA when he passed last year. She had Disney stock, and an S&P 500 mutual fund. She trusts me, and neither DH nor his brother know much about investing.
So I queried BIL's comfort on various topics; as expected, he was not supportive of foreign investments, so domestic MFs it is.
As a result, we put 45% in Vanguard Wellington, and 45% in Vanguard Wellesley. And 10% in cash, so we can transfer funds quickly, without selling and settling anything.
That gives her 45% domestic stocks, 45% domestic bonds, and 10% cash. She's at Schwab, so did pay a $75 one-time fee for the purchases, but we were OK with that.
If you wanted some international representation, Vanguard's Life Strategy Moderate Growth fund (VSMGX) would be a good choice: its ER is .15%, and it has Domestic stocks + bonds, and Foreign stocks + bonds. You'd never need to rebalance, as they do it for you.