Amanda gave you all of the answers. One concern and I do not recall 100 percent the outside paths through the garden are a mixture of sidewalk, dirt and cobblestone. Some of which may be difficult to push a wheel chair.
Yes but the wheelchair accessibility is around the back of the buliding. Also you will be able to access most of the conservatory except the top story
Yes
There is a ramp to the top
Yes there are wheelchair ramps.
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