crumbling grout and hollow coping

I need some advice. We have an inground guinte pool with bullnose coping and a cool deck that was installed directly up to the coping. There is no expansion joint. The grout between the coping and the waterline tile started pulling away from the coping and now has started crumbling and needs to be replaced. If you tap on the coping it sounds hollow almost all the way around the pool and a few are slightly loose (can be slighlty moved but not picked up) but the rest seem to be secure although hollow. No tiles are cracked or popping off.
A few questions for yall...
1. Does the coping need to be removed and replaced or can it be left as is, and if can leave it should we squeeze some mortar under there before grouting?
2. Do we need to have an expansion joint? We have talked to several pool repair guys who have all said that nobody does that anymore and refused to even consider repairing our pool if we wanted an expansion joint.
I was thinking if we could just replace the grout between the coping and tile and put in an expansion joint and sealing it we could avoid tearing up the coping.
What is everyone's opinion and/or ideas to handle this situation.

Any advice? No one wants to help?

Hi - I have a simular problem - what did you end up doing?

Most of the posters and all the moderators here are residential pool owners, not pool builders. Even most of the pool guys here are service guys (like me), not builders.

So, when you ask a builder question, here you may or may not get an answer.

You can try at poolspaforum.com -- there are a LOT of pool guys there. The problem for me is, if I let them in here, it seems most (more than 90%) can't tell the difference between "helping" and "selling" . . . and most of them want to answer chemical questions, even though much of what they 'know' about pool chemistry is wrong.