Kitchen renovation - load bearing wall

We are planning on installing new kitchen which includes some minor renovation work and could do with some advice.


Background:

Kitchen was previously extended with a single story extension which along with kitchen, spans the width of house (approx 24ft). The room is then divided into kitchen / dinning area which we want to open up and this is where we are hitting issues as we are getting conflicting advice / costs from various builders.


I have attached some pics of walls and labeled:
A - (within extension half of kitchen) possible load bearing wall

B - (within original kitchen) is just a stud partition with archway

Plan:

The first dividing wall we want to remove (within original kitchen) is just a stud partition with archway, this should be fairly straightforward to remove.

The second dividing wall we want to remove (within extension half of kitchen) is what causes confusion, as we have been told it "may" be load baring. This wall basically just divides the single story extension in half so has nothing but the roof of extension above.

I should mention that the kitchen already has an RSJ from when extensions was originally built and pillar in center of room. We hope to create some island feature around the pillar.

Some builders have suggested removing pillar and install of new RSJ but want to avoid this cost


Advice:

Any advice on who can determine if wall can be knocked. A structural engineer? or surveyor? and also, with the renovation work required we would like to get some plans drawn up so we can just hand to builder.


If it is a case the wall is load bearing we are also considering creating a "pass-thru opening", rather than knock the whole wall and try incorporate an island feature into the opening.

Thanks.