My little guy still has 3 bottles a day with daycare, only two with me usually as I am a bit more persistent with other foods and his water to fill him up mid-day. I haven't tried milk in the sippy yet because I'm still mixing in a bit of formula. Maybe try a different sippy cup, one unique just for the milk. Only for the afternoon -- offer it but don't push it, sort of leave it around for him to find and drink (not too long since its milk lol).
I agree with the sleep, don't fix what is not broken. Should he start to be a challenge to get down for two naps or if his night sleep starts to suffer then consider adjusting.
Good luck!