Keeping family heritage plants is always important - many cultivars are unavailable now and they're a way to memorialise people.
Based on your climate, it seems they could be moved anytime between Spring and late Summer. Other times may not allow the plants to grow a suitable
root system before Winter. (Harden off)
Regardless, ensure you take a large rootball with dirt attached, cleanly trim any
roots with sécateurs to avoid disease, and trim the plant back a bit to lower transpiration. Wrap the rootball in hessian (it breathes) and keep moist.
Get them into the new spot soon thereafter, mulch with
compost and
water in well with dilute seaweed/fish liquid fertiliser - not actually a fertiliser, more of a soil conditioner increasing microbial activity.
Avoid using manure or other fertilisers until next Summer, it could caused fertiliser burn.
(Also, when transporting in a car, cover them with a tarp or cloth to avoid wind and sun burn.)