Q.1 : If buried with a person, should they be a layer below the coffin rather than in the coffin itself ?

A.1 : Whereas a single book might be placed in the coffin, in this instance several tens of books will be involved and this will not be practical; they should be placed in a biodegradable bag and lowered into the grave before the funeral begins and the mourners have gathered (unless they particularly want to have this as part of the funeral service), then soil added to cover them and produce a level layer of soil, after which the funeral can proceed as normal in its own time.

Q.2 : Might there be issues with the cemetery authorities where our cemetery is part of a larger, other faith(s) cemetery?

A.2 : I do not see why they should object, especially as the plot usually 'belongs' to the person who bought it (be it the deceased or their relatives) and I assume the relatives would have been consulted beforehand (which they certainly should be) and would have approved of this (and considered it a special honour).

Q.3 : Alternatively, could a separate hole be dug to bury siddurim?

A.3 : Yes, this is also possible if you don't want to wait for a funeral or wish to have all the books together which might not be possible otherwise, although this would be using up a potential gravespace and might be considered wasteful - unless there was a spot that was available but not suitable for a burial.

Q.4 : Should that be in the cemetery?

A.4 : Yes, although as we are talking about burying books, if you have a synagogue garden, maybe it would be appropriate to bury them in a special section there

Q.5 : If so, again: any issues with the authorities?

A.5 : I cannot see why they should object providing the synagogue had purchased the gravespace, while if it was in your own synagogue garden then you have control over arrangements.

Q. 6 : If buried elsewhere, would it have to be on shul land ?

A. 6 : I would have thought that the cemetery or synagogue grounds would be the obvious place, although you could use other communal areas, such as the grounds of a Jewish day school and have a properly marked section there.

Q.7 : What are the (additional) rules/ procedures/ prayers to be observed ?

Q. A : It might be appropriate (and a good exercise to involve both young and old members of the community) to compose some prayers in English expressing the significance of the occasion, perhaps sing 'Etz hayyim hee' and say a communal kaddish for all those members of the congregation who once used the prayer books but have now passed away.