2nd choice doesn't matter in the slightest if preference order isn't in the admissions policy.
Example - you apply to schools 1 - 5. Somehow (pure luck) you 'win' a lottery place in every single one. You only receive an offer from the school you marked #1 because the others are automatically removed - because you got a place at #1.
Example 2 - you apply to schools 1- 5. You win a lottery place in #2, #4 and #5. You automatically receive an offer from #2 and the places for #4 and #5 are offered to other families - because you got a place at #2.
Most people who don't have a place at all only applied for #1 and #2. They fail to get a lottery place. They haven't put any other schools on the application. They then have to take what they're given out of all the other schools with spaces after all the acceptances are in. The leftovers, basically.
Not filling the applications fully out of a misguided idea that it's better to apply to just 2 in the belief that it matters to Admissions that you're prepared to risk having nowhere is the reason why there are kids without anywhere to go to at present.
It's like wanting to win a prize in a raffle. Five draws, one at £10, one at £100, one at £1000, one £1500, one £10,000 and one £20,000.
You don't have to forfeit the higher prize entries if you buy tickets for the others. But the rules are that you can only take one prize if you win more than one, which is the highest payout.
If you decide not to buy tickets for the draws with prizes of £1000, £100 and £10 because you'd far rather win £10,000 or £20,000 prizes (who wouldn't?), you aren't going to end up with anything if somebody else's ticket gets drawn in the two higher prize draws.
Apply for all five in preference, be ready to ask for a place on the waiting list and start the appeal on 2nd March/whenever the offer day is next year, go for entrance exams for private if that's something you can do and your DC can cope with, but it's far less likely you'll be left without anywhere at all and have to take a place at literally the one school that almost nobody wants to go to.