No photos are showing up. I think in the very long term they might be harmful. They will grow as epiphytes and not parasites so their roots will just run down the palm trunks into the ground. But they can become fairly large trees and that could interfere with the palms growth.

Thanks for the advice. I have added some photos.

Whether they harm or don't harm would be secondary to me. First, I'd question if I wanted an appearance of other trees combined with the palms, since the palms have such a distinct look. It could go either way.

Those do not look like Schefflera to me, more like a Ficus species, as in Strangler Fig. Yes they will hurt the date palms if left. Get them out now while they are small and it is easier to do.

I'd agree, that looks like Ficus and not Schefflera. From what I can make out of the leaves it would be Ficus benjamina. I often get seedlings come up on rocks, logs, trees and in flower pots. Birds eat the fruit and spread the seeds around. Palms won't succumb as quickly as other trees but the earlier you get them out the easier it will be. There's no practical way to prevent birds from bringing more seed in so it'll be an ongoing job picking out new seedlings.