Your little boy sounds like a lucky little man! It must be wonderful for him to have so many loving people to play with! TBH he sounds like a very normal 18 month old. Most are very demanding of your attention so it's hard to say if it's because he is being entertained so much. It is very normal for them to be extra-demanding while teething too.

Every child is different and some are more happy to entertain themselves than others. You could give him little activities to do on his own to encourage him to play by himself, maybe try and do this at least once a day so he becomes used to it. Tell your parents that it's his time now, but they can play with him again in 5/10 minutes (whatever time you decide is enough).

But honestly, he sounds pretty normal to me