your right
they are where they are because of the T offs.
is the top one on the drawing going to interfer with the conservatory base, I take it you could be going full width of the house.
If so then you will have a slight problem, it could be moved to the left so its behind the other one and then you will have to continue the pipework to existing, then fit a rodding eye
OUTSIDE OF THE CONSERVATORY BASE behind the T point so you can rod both ways if you know what I mean. A rodding eye is quite small as well so easy to install.
When you dig out for the base this can all be done at the same time to save mess and upheaval.
One point to remember is when the footings for the new base cross the pipework the brickwork above must be supported with concrete lintels as it crosses the drains, not a big or expensive job this though.
If its gonna be a double skin dwarf wall for the con you will need 4 lintels to support each wall and its cheaper to buy one long one and cut it to length with a still saw. 50 quid will do that easy.
Hope thats helps you mate and if you need to ask owt else fire away
cheers Al