A single earner, high salary family isn't the likeliest of candidates for a bursary.
Your second DC hadn't started school yet. They may well expect you to have started earning by then, so bursary will be unnecessary.
There is no way you'll get a bursary on the basis of being unwilling/unable to pay for 2 simultaneously when you have only one in the school.
They are highly unlikely to commit to a bursary now, when it is 2-3 years before your 2nd DC reaches school age.
Qualifying for bursary on a salary of £90k, even if it were combined income from two working parents, is also unlikely, as it is over the earnings threshold for many (I'd say most, and would want to say 'all', but sineine might turn up with a counter example)
Parent being a former pupil carries little to no weight.
You need to make some different choices if you want this school for your DC. I mean apply but, realistically, high earning families such as yours have to pay.
Many people have been priced out of private education. You're not in unusual circumstances.
You are however lucky - you can make different decisions if it really is your central dream. You need to put the business on hold and get back into the employment. You cannot afford both school fees and for you to bring in nothing. So get back into work now, and save as much of your pay as possible towards fees and other school costs (such as uniforms).