They are generally surface rooters so you can essentially get a fork or spade under the top foot or less and lift out. The end.

Mature rhodies can be cut almost to a stump and can generally resprout along the dormant buds. Old, overgrown rhodies are often rejuvination pruned like that. My mother's near 40-year old ones went through some rejuvination pruning last year and are coming back nicely.

If you have fern and rhodies, then the area seems to be fairly shaded. How much sun does the property get? If it is shade, look for other shade tolerant bloomers such as their relatives the azaleas, perhaps even some cold hardy shrub fuchsias, hardy camellias, etc.

Jenny is correct about Rhodies to be easy to remove and well responding to rejuvenation pruning.
As to your Rh + Fern site, I could venture a guess that it is not only shady, but also a moist site.
If so, Clethras will thrive there and will provide you flowers from July till September depending on cultivars you chose. Also, Clethras, while deciduos, have a pleasant framework for the winter view and easy prunable.

There is a very good chance your older established rhododendrons will resprout after being cut to ground level if they were healthy vigorous shrubs. If you want to replant the area, you'll want to remove the stumps/root ball.

While it's true these are mostly surface rooted shrubs, you will also find heavier woody roots supporting rhododendrons of that age...not all of these will have to be removed (think ax) but some digging will be required. I don't know what kind of soil base you have, but my clay based soil is much too wet to undertake that kind of project this early in most areas of my garden. I don't assume you have the same clay base, but if you do, working (tilling, spading, digging) wet soil can actually damage soil structure. Soil that is too wet when worked will compact into concrete-like clumps that will be with you forever.

Since many rhododendrons and ferns like our native sword ferns do well in full sun in the PNW, you haven't given enough information for shrub suggestions. The choices in this mild climate are almost endless, with much to consider - the ultimate height/width you would find attractive, bloom time, color preferences, evergreen or deciduous. Do you know yet what kind of exposure they will receive if you moved in Sept? (My north facing back garden is in a great deal of shade Fall through Winter but gets almost full sun late Spring through Summer.)

I don't know exactly where you are located, but there are many exceptional nurseries and several with display gardens available to gardeners here.

40 year old rhodies don't come out easy. Since it's right next to the driveway why not hook up to them one at a time to a large truck and pull them out?

Most large rhodies can be pruned to look like a small tree that can be seen through, rather than an overgrown, out of control bush. When pruning them like a tree, in most cases you don't even have to take anything off the top. You do have to consider snow load though. Why not try it on that rhodie that you "want to prune it back and shape it nicely"?

Older hybrid rhododendrons here are often grafted onto purplish-flowered, shiny-leaved Rhododendron ponticum. This often sends up plenty of sprouts of its own, can be seen to have partially or completely overwhelmed and replaced the hybrid cultivar that was grafted onto it in more than a few plantings. If you check for this next spring you may find you have the same thing going on, in which case the rootstock sprouts should be cut out, unless you have plants that are too far gone/prefer the Pontic rhododendron.

Good companions for rhododendrons are Japanese maples (unless your place is infested with/becomes infested with Verticillium wilt), Mahonia aquifolium (foliage blends with about anything), Pieris spp., Hamamelis spp., Vaccinium ovatum, Enkianthus campanulatus, Fargesia spp. (and other delicate-looking, clumping bamboos), lilies, hostas, primroses and other woodland garden favorites.

Thank you all for your suggestions. My husband is working on getting the stumps out, chunk by chunk. I was afraid of them resprouting...I just don't want them in that spot!

We've only lived here a very short time, so no idea, yet, of how the sun works, but it's got a nice southwestern exposure, but there are LOTS and lots of large, mature maple trees providing shade.

Rhododendron ponticum is also considerd a invasive species in many countries and may be a threat here aswell. I beleive this is the only rhododendron that is invasive.

I wish I had gotten around to this question sooner. When, if any, is a good time to cut back rhododendrons? These are very tall (like 12'-15') and I would like them back to around 5'. I prefer not to kill them so must I wait until winter for pruning? Thanks, Gene

Prune immediately following bloom.

Rhododendron ponticum doesn't choke woodlands here like it does in parts of UK. Probably can't reproduce under our dry summer conditions, without irrigation.