Honestly, though a lower instrument will be better on the ears of those who don’t like the whistle, i think overall you’ll find that, if the music is annoying now for people, it will be slightly less annoying but ultimately still annoying for those who don’t want to hear it. Case in point, my wife hates my whistling similar to the way you’re talkign about your family and neighbors disliking yours, and it got so bad that once, in extreme annoyance, she threw and broke my Bb gen. (Luckily, i’m a fairly patient person and we worked through that one.)
I figured that it was the high pitched sound that was bugging her, and in part it was, but that wasnt the only thing. When i bought a tipple low d flute, decidedly lower than the whistles i’d been playing, she remarked that it was less piercing, and that she liked it better… but my playing still annoyed her almost just as much, lower pitch and all. It really was the music she didnt like, the genre, the tunes, the whole “irish” thing (even though she’s part irish herself, go figure). My mother, who lives near me, has a similar dislike (“I like the sound, but can’t you play something other than leprechuan music,” she said)
Now, my mom is a musician herself (piano for 48 years) so even though she dislikes the style of music, she can appreciate my desire to play, but not so my wife. What really got my wife to stop being so annoyed with it was not the lower pitch, but really i had to sit down and explain to her how playing it made me feel, how much i enjoyed it and the beauty it added to my life and such. Once she understood how much it meant to me, she was more willing to deal with it, to be supportive, even, even though she doesnt care for it. Ultimately we had to compromise. I can play an hour per day at home and she’ll bark no complaint. Now, that isn’t nearly the amount of time that i’d like to play per day, but it is something, and since i play at work for about an hour or so per day while grading and after school (sometimes staying late just to play) it works out for me.
I’d really, though, suggest firstly, not quitting. You’ll miss it, and the beauty it brings to your life will be missed sooner or later. Also, it could create resentment in you for some of those you care about. SEcondly, i’d talk to those you care about that don’t like it, let them know what it means to you. Maybe when they see or understand what it means to you, they’ll be more understanding.
Another thing, it might be advisable to practice for a set time or a set amount of time per day. I know one of my wife’s big annoyances was that i would walk around the house with the whistle basically all day, playing a minute or two here, a minute or two there. THough overall i may have totally played like an hour or so that day, the fact that it was spread out at sporadic times of the day gave it the feeling that i was playing all day, making her listen to something she didnt want to listen too all day long.
As for neighbors… i dont know, i don’t live in an apartment, though my neighbors who are friendly say that they occasionally hear it in their house, especially the louder whistles. I try to make sure i dont play too late too loud, so i dont wake them (the husband drives trucks, leaves at like 4 am) or too loud too early. I have some down the street neighbors who blast their stereos, sometimes late at night, and it’s super annoying to me, so i try to avoid being like that. I wouldnt stop, though, because my neighbors didnt like it, i would though try to be courteous and considerate, within reason (i.e. no 2 am susato loud as you can blow sessions) but ultimately keep playing.
You may, as suggested, consider getting a lower pitched whistle. Though it may not take away, ultimately, the annoyance, it may blunt it a bit. My wife hates my Bb as much as she hates my Eb, but it took her a little longer to build up that hatred 
