Well yes, that's generally what business have to do if they can't find other ways to increase revenue.
I mean I've made some assumptions but if;
10 of the 50 are on NMW FT (admin staff)
10 on £25k (nurses, new vets)
15 on £35k (average for a vet)
10 on £60k (higher end for experienced vets)
5 on £100k (highly specialized vets)
Then the changes to NI and NMW would result in around a 2-3% increase in overall staffing costs.
If that's enough to put people out of a job then he clearly wasn't planning to award even inflationary pay rises this year to his staff, and I've no idea how he made it through the energy crisis with such small margins.
The fact that you stated there have been opportunities to sell the practices to larger business suggests there is scope for increasing profitability.
I'm sure your husband is a fantastic vet and it sounds as if caring person with the best interests of his customers at heart, unfortunately that doesn't mean he's a good businessman.