You’ve certainly in your initial post phrased things in a way that one could misinterpret your plans as “getting at least as good a deal as the RAV pays out otherwise”.
Even just your chosen topic title could be misinterpreted.
Anyway, no judgement passed.
You OH needed more than 6 months to find a job that pays less than 80% of the prior job. You should take the job and do whatever you can to get it as smooth as possible. No reason to think whether it was the laber market or your Oh‘s profile but clearly, the OH is (at least currently) not fit for the labour market.
Where do these deductions come? The new role pays significantly more than the previous role she had did.
That’s what we are trying to do. But also we have family planning and booked vacations.
Well, that’s great for you to say. You seem to be knowing well the job market, her profile and her gaps. But you also must be aware already how many parallel processes she has actually in the last stage.
Well done on the empathy skillz 
Thanks for being civil about this and flagging things that might have gone misinterpreted. I’ve reformulated the topic name and the opening post to be more clear.
But I think at this point the topic is as good as burned with judgement either way. 
To sum up the options:
You mentioned the new salary was below the rav 80% and six months plus of unemployment? In such situation, I would really not play too much with the employer. Accepz the job nut make it clear when you had vacations - and ask for their proposal on how to take them (unpaid or as a sign-on bonus). I wouldnt try to negotiate something strange that may make the employer withdraw if you were unemployed for 6+ months. The employer may very well think you tried to cheat on RAV (that is still my conclusion from this treat - and then just stop the entire process for ethical mismatch.
The post reads better now, but some of your comments are the ones that sound judgmental and passive aggressive. Typically, that doesn’t help with getting any response, but I’ll do one more. But let’s keep it at that.
That’s not correct. If RAV would know they could start now, but don’t want to, they’d cut payments. You booking trips or not lining up options for child-care during school vacation is not on RAV. I’m not judging here, it’s just the rules.
Would it go unnoticed if the company plays along? Probably.
Is it understandable you want to take advantage and enjoy the time off? Yes.
But is it judgmental to call out that it’s a mis-use of the system and should not be encouraged here? Well, I am kind of judging the attitude, but I guess you made your peace with that and I’m not sure I wouldn’t consider the options in the same situation.
Alright, so the only morally correct option remaining seems my point 2 with granting full yearly vacations despite starting in July (which is a Yes/No approval on the same contract and 1 clause, so easy to administer) and then it’s a clear cut and everyone is in the clean.
Seen differently, she might just get the unpaid leave and get compensated with a sign-on bonus, that’s also an option.
Alternatively, she could start in August - this case has been confirmed with the RAV person last month, they also said you can skip the application process in the last month as long as you have a signed contract. But alas, she already verbally accepted the offer that hinted on 1st July start… the stance from the company was that “we’ll solve it somehow”, but I’m sure they have no clue on how to “solve this” other than the employee go out empty handed on unpaid leave for being kind to the company.
In my dictionary, ‘solving it’ would mean this limited temporary contract, but this might give more questions than answers on the “why”. Plus it sounds complicated (getting another contract, plus approvals, plus agreeing a daily rate, plus how to report vacations, what to report to RAV, etc - lot of fuss).
She’ll have a sit-down with the HR person in 2 days and a RAV appointment right after, so rest assured we’ll keep it as clean as possible.
Thanks for the constructive points, appreciate you came back with facts instead of more judgment. 
No, I factually never mentioned this (again, I feel you’ve already put her in the “cheater” bucket and you couldn’t be further from the truth).
I said if she were to start working 1st July, then took all her legally allowed vacations, then took some more vac unpaid to cover the rest, she would get less money than not working on these “vacation weeks” (and thus being on RAV), only because unpaid vacs are pretty “expensive” as a damage.
Honestly, without a written proof from the RAV that there are ok to pay untill August precisely to let your relative go in holidays, I don’t support any option that involves an delay start. It’s a major risk to be awarded with an >30 days of penalty.
Waste of time, either accept the conditions of the job start date or go on holiday instead. This is a bit like deciding what to eat for lunch