Plantomaniac, That is a lovely variegation on your parlour palm. Like with most Neanthe bellas bought from stores, your pot seems to be full of many different seedlings. It might be worth checking to see which one this leaf is springing from, and if the variegation continues, perhaps you could gently separate it and grow it on on its own. In that case, when you move it enclose it in a plastic bag until you're sure it has 'taken' to its new home.

10C or 50F is not a chance for a Washingtonia. I went through that and gave up 7B/8A climates and long terms survival for any palms other than Trachys, Sabals and an occasional Butia. Even in zone 11 here they don't look at their best. My Washingtonia was killed at 14F just one night of 14F and one day of 30F was enough for all my Washies. In fact Wash. filifera is not doing well in a rainy climate or a semi-shade or both, I would not take a chance either in a rural area zone 8 with any of the Washies. 8 years experience talking. Now I am in a zone 11 without much heat, so it may not be a true zone 11 since the low temps March the 11B but high temps are never above 80F. Even the 80F is reached a couple days a year for short periods. I would say Washies are best for zone 9 and up, maybe marginal for 8B. That's it. Your Washie is dead or dying and even if it comes back, it will not last long. The next winter will kill it. It is now too weak to survive. Move to a warmer zone. I lost too much money playing with borderline zones. Get your plants one or half zone below yours and you will be safe.

Mangos are like the most common fruit tree here in St. Pete. I see them everywhere. They're way more common than any citrus. Some of them look ancient. The one in the old tread below isn't far from my house. https://www.houzz.com/discussions/huge-mango-tree-central-florida-dsvw-vd~4173398 Another tree that becomes mammoth here is lychee. I've seen some with canopies bigger than any other tree in the neighborhood. I think I remember seeing mature rambutans here too but I'm not absolutely certain. I've definitely seen smaller ones planted out and they're often sold at my farmers markets along with many other exotic trees, rollinia, jackfruit, soursop, etc.

How it looks. You can follow up by looking at your palm with a magnifier.