Confusedgranny We all, at any age, have expectations/ideas/dreams of what a particular period in our lives will be like. When those expectations are not met it is hard, painful, challenging to accept. It is hard when we find that what we thought we had isn't quite what we expected it to be, too.
You have obviously brought up a son who has the confidence to make his own life with his wife and his children and who is creating that life in a way that works for them; that is an achievement for you. Perhaps your son seems selfish, lacking in thought for you but then don't you think children always tend to assume that parents can cope ...we coped when they were young (they won't know how hard it was at times!); they assume we will now! And none of us know for sure what our children have to deal with/negotiate in their own lives and relationships. I expect you had to do that too, in relation to your own parents/PIL. I know I did.
Did you decide what you needed from your own parents/PIL for your children? Again, I know we did! Both sets of parents offered different things; giggling and cookery from my mum; "intellectual" type conversations from my dad (when the kids got older!); football/sport madness from my FIL; general chat and little family history conversations from my MIL.[who if I am honest, was very difficult at times!] My parents had them to stay very occasionally, my PIL babysat a couple of times. We lived 2 hours away from my parents, and then 50 minutes away. 3 1/2 hours away from my PIL. We had very busy lives, we did make a point of inviting them and going to see them when we could. We spoke on the phone weekly. Both sets of parents helped to maintain that, a quick ring to see how were etc. if we hadn't rung, but not too often. These days quick communication is easier with texts etc. too
Maybe it would help you to think back to when your son was young and how you as a parent responded with his respective grandparents; your expectations of them. Yes, your expectations might have been for them to be more hands on etc. Maybe you welcomed the help etc. But if your son and DILs expectations are different then that is up to them and you have to fit in with their expectations of grandparenting, otherwise the relationship will be likely to deteriorate further. That would be so sad for you.
Try to think about the positives in what you DO have as a grandmother, not what you don't have. And DO please take the advice about the hotel, if you truly feel they are not keen on you staying; it may seem daft, but if it is best for them then so be it. When you are there, can you take something that will interest your grandchild...something that logically you might do with him? Maybe a little pop up book - 3 year olds love them. Or a Duplo toy to make together? Make yourself interesting to him; DIL/son might like to see him enjoying something with you, rather than you trying to do what is part of their routine like bath time.
I hope that you can move forward positively with this so that your grandson can experience a positive relationship with you and also observe a positive relationship between you and his parents