I’m assuming the business is a Ltd?
You’d need to do some planning now with the shareholdings - on the assumption you can claim BPR and Holdover relief and no immediate tax issue. This (HR) would need to be considered if the business was sold. Leaving that aside -
The owner could gift 70% of the shares now to the 2 business people.
A Class Shares.
The remaining 30% would be split between the owner, his wife and daughter.
B Class Shares.
Wife and daughter would be Directors and could receive dividends. (Income) from the B Class shares.
If they wish to sell then ‘the sum’ would be paid on winding up or liquidation of the B Class Shares.
You’d need the above drafted in either a shareholder agreement or by alteration of the articles of association.
To retain some control of voting 80/30 the B Class shares can hold weighted voting rights - for example if the A Class share holders try to remove directors, alter the articles etc.
The rights on winding up can be specified for the each class of share - % of the nett sale proceeds.
The rights to dividends again can be specified in the articles - % of profits.
The downside is you lose the CGT uplift on the owners death. The owner needs to agree with gifting shares today and the possible implications of that.