Advice needed

[MickyEngland]

I've a couple of questions I'm hoping someone is able to help me with.
I'm currently doing some home alterations and knocking my kitchen and dining room into one open plan kitchen diner. I would like to be able to turn on the two ceiling roses by either of the 2 switches, currently the switches only operate one light each as they are 2 separate rooms. It would be great if someone could either explain or draw a diagram for me please.
My second question, I have taken out an electric shower which has a long run of 10 mm twin an earth connected to the fuse board, could I use this cable to supply power for 2 ovens or 1 double oven. I've left the cable in the ceiling joists above where I intend to have my ovens.
Any advice would be appreciated thanks.

 

[poni]

last question first, yes you can use the 10mm T&E for what ever you want as long as you don't over load the cable ( that is hard to tell you as we need more details,) but normally 10mm is good for about 45A, look at the consumer unit and see the fuse/ MCB size it is , that would be a good indication ( if it was install correctly,again we will not know)
the first question is a lot harder to explain then it is to do, first you need to remove one ceiling light from the circuit( put the old cable in a joint box and label them as old light, remembering to not connect the switch pair) then connect it to the other light using some T&E the same size as the existing ones. both switches will need to be changed to two way switches, the switch that controls the light that has been removed needs a cable run to the other switch this should be a 3core and earth the same size as all the others,