This is my current team: Spirit is my tank, Ashlynne is a heavy damage dealer, and Siren is support.

Noctus, Un-named 1, and Un-named 2 are currently acting as mission pets, but I'm wondering if I shouldn't put one of them into my battle team to help deal with the challenges that I'm facing in the lost grove. I also need to decide what element to attune Un-named 2 to. (I'm also still looking for names for them if that's something you are interested in helping with.)

Does anyone have any advice?

The grove gets easier as you go. You should focus on unlocking the Barracks building which helps gives your pets bonuses which is incredibly helpful with bosses. Choose your pet party and develop them- the Grove gets a lot easier as you battle through it because your pets battle abilities will rank up (this is a very grindy task). Work on getting your pets the Vinethorn gear in every slot. At this point, I can go in with pets with a tamed stats team (Bases of 10-20) and be perfectly fine because a.) I know the attack patterns, b.) I have the bonuses and c.) they have Grove equipment.

the only thing I would really suggest is swapping Ashlynne to 3int/1dex.
You could maybe swapp Siren to 3str/1agi (I have never used a water support) and/or Spirit to 1HP/2str/1agi, even if just to test it out for a bit and see how it works

(my own earth tank was either 2str/2agi or 1str/3agi, I think, before we hit lv70 and swapped to 1HP/2str/2agi, but I feel like Tanks are the pets with the most personal setup for people and what works best for one person may work badly for another?)
(fighting in the LG means sometimes shuffling pet profs just to see if you can get it to work better, working out what prof setup works best for your own battle strategy- I had to alter the water tank we're using's profs like, five times before we hit on a setup that worked for us)

Higher str stats, though, mean that the pets are more effective overall with their power- thorncoat and ice barrier are more effective because they absorb a bit more damage/deal a bit more damage (in thorncoat's case). On the fire pet, you already have two pets that are protecting her- earth drawing attacks to itself, water with ice barrier, so she doesn't really need the HP


But yeah, it definitely gets easier as you continue and ever-so-slowly manage to level up the ability ranks. It is an incredibly tedious grind, but well worth it.

If you have trouble with enemy mobs, you can spend time grinding in the top area of the grove, where it only spawns 1 enemy at a time