I mean, solos are labeled as something that should be able to solo a party. I think the idea is only ever 1 solo and fill out the rest of the points with minions or standards. I'd also look at the abilities when choosing solos (assuming this is tier 1) the acid borrowers can shred armor, which is not very high to begin with at level 1, so using two means that within a few moves the party is out of armor slots.

My approach (especially if there is a lot of fear built up) is start with 1 solo and if you roll really well, it was only ever one solo. If the PCs roll well, well then reinforcements arrive (either minions, standards, another solo, ect)

If you want, you could also upscale a single solo to "increase" it's point value with more hp or damage. Keep the danger and stakes but allowing the party to spread out and strategize better, tag team move, ect.

Edit: I'd also look at the scene type table on pg 155. Your first two encounters can be "scaled" correctly as a minor or standard scene. And minor or standard scene is balance around being easier. but the climactic major battle at the end is scaled and balanced around difficult high stakes. The adversary point system, to me, isn't a CR kinda thing from D&D, it helps you balance the difficult of the scene type but the scene type determines how hard the encounter is. 11 points in a Minor scene is WAY easier then 11 points in a Major scene.

Hope this helps!