If you do not know how to hand-feed, it is safer to leave the feeding and weaning to the parents, but this may delay socialization of the babies, as they will likely view humans as unfamiliar and unsafe, in comparison to the familiar care they receive from their parents, by the time they are fully weaned. To my knowledge, socialization by humans, in this case, cannot begin until the babies have been fully weaned by the parents, but I'm not familiar with attempting to handle babies from the nest, while they are still being parent-fed. Not sure if other members have had experience with socializing babies while they are being parent-fed.
Is the 1.5 month old now eating on it own? What diet are your birds on? For Lovebirds, a mix of pellets and seed with fresh fruits and vegetables is recommended. If the 1.5 month old is eating on its own, I would separate it from his parents, placing it in its own cage with toys, where you can begin socializing it. You can begin by spending time with the babies in a different room from the parents. Talking to them softly, over time, will allow them to become accustomed to your presence, and then as I described in my post above, continue by offering it treats by hand, or even hand-feeding from a spoon to begin engaging it in human-fid interaction. Placing a favorite treat, such as millet, hidden in your hand, where the baby can see it, may entice it to attempt to pry it out from between your fingers, and this exercise may ease the bird's fears of humans over time, viewing human hands as rewarding. I would do the same with the two week old baby as soon as it is weaned. Good luck
