It's always tough trying to find a hedge that will grow in sun and shade, especially when you want a uniform look. Having said that, it isn't uncommon for designers to use a couple of different species - for example one species to boundary fences with another to the front fence. I'd consider lifting the canopy of the existing trees to let light in for more even growth across the hedge, however I'd still expect it to be a bit uneven due to the varying conditions throughout the garden. Viburnum tinus is a good pick for both a sunny position and a shady position, it will eventually get to 2m height and can be kept as low as 1m. If this isn't large enough, you could also try Portuguese laurel, (Prunus lusitanica) which will get to 4m easily enough. Both of these aren't particularly fast growing, but with adequate water and food they should be good for your situation. Murraya is another one that will tolerate sun and shade, though not frost. You won't get as many flowers in shady positions, and it may look a bit straggly. Your local nursery may be able to advise on what is readily available. When you plant, preparation and ongoing care is going to be important as it look as though you have a few plants that the hedge will have to compete with as it establishes (your neighbours conifers and your pears). Digging a good wide planting hole, plenty of organic matter mixed with the back-fill, as well as regular watering and feeding until the plants get established. Much as the Flower Carpet Roses are tough (especially the original pink), I wouldn't recommend planting roses in anything less than 4 hours of direct sun a day. You'll end up having issues with blackspot and mildew, and they're not going to give you the neat box look that you want. Flower Carpet Roses (Tesselaar Roses) are a good tough rose, however some colours (cultivars) are tougher than others. Pink is one of the best performing varieties, and as suggested, reaches a bit more than the height on the label. That may not be true of all the different colours though. Be careful propagating any of the flower carpet roses, only ever for yourself as they are rigourously protected either with trademark names and/or Plant Breeders Rights, making it illegal to sell the propagated material under the flower carpet name, or at all (in the case of PBR). Good luck!

Cost depends on pot size, so the larger the plant, the bigger the pot and the more expensive. The smaller potted plants are usually much younger so take a few years to get to the same size as those available in the larger pots. If you are buying in bulk you should negotiate with the nursery as some will include free delivery with orders over a certain value, or a certain number of plants. Check out these guys who have a reputation for cheap prices, but I can't personally vouch for their quality. https://www.thetutuguru.com.au/shop/everscreen-ornamental-pear/?utm_term=&utm_campaign=Product+Listing+Ads&utm_source=adwords&utm_medium=ppc&hsa_acc=2747650483&hsa_cam=207373465&hsa_grp=14195360425&hsa_ad=51716088145&hsa_src=g&hsa_tgt=pla-18283950120&hsa_kw=&hsa_mt=&hsa_net=adwords&hsa_ver=3&gclid=CjwKCAjwguzzBRBiEiwAgU0FT6VHZnrXEw9LM96QVKzQ5IqDPPX4yR_NPvQ_xwRkOfuUUV09HfUb8RoCPa0QAvD_BwE Best of luck, Dr Retro of Dr Retro House Calls

Pop over to Pintrest and search “Pleached trees with hedge underneath”, I suspect this is the look your landscaper is looking for. Eg below. Plenty of examples of trees planted amongst hedges. Rather than ornamental pears, have a look at grafted/weeping/standard grevilleas. They fit with your native hedge and will have similar water and food requirements plus they give you some height straight away. And have foliage all year around.

Yes absolutely, cut them up in line with your fence and leave the canopy on the inside. I usually cut ours when they are deciduous but if you think the council will get to them before then , then cut them before they do.