if the HC is pearling the lighting is fine, ive tried lilaeopsis brasiliensis, and i have never had any luck with it, it can be extremely difficult, L.Mauritiana is an easier option, but does grow slightly taller, also for the otocinclus they can be very hard to get to eat the first few days, so i would put in some veggies for them or algae wafer, thats all you can do and just hope for the best, test all your water conditions before getting them as they can be quite sensative.
the main thing with plants is patience, give it time, also i would get some fast growing stem plants in there before the algae takes hold, you can get a pack of 50 from greenline for like a fiver.