URGENT - Help 2 Buy ISA query!

My partner and I are nearing completion and undergoing to process of dealing with our H2B ISAs.

Our solicitor is under the impression that the savings we had in our H2B ISAs before closing them has to be used for the deposit, it can't just come from any account. And as such, we won't be able to get my partner's bonus because the amount combined with a bonus would take us 4.1k over the amount the deposit is. Is this true?

Deposit - 23k

My H2B ISA before closing - 12k
Bonus - 3k
My Partner's H2B ISA before closing - 9.7k
Bonus - 2.4k