Can they be planted to the right of the existing maple and spruce within 2 to 4m of them without interference of the established roots systems?
Thank you for contacting the Toronto Master Gardeners with your Yew planting question.
Planting within this 2-4m distance of two established trees should be fine as long as you are careful when digging the holes for the new additions – any larger tree roots should be avoided or carefully worked around. Hand digging is preferable over mechanical digging so the site can be constantly assessed and monitored for inadvertently cut roots. Water the new Yews in well and continue to water every 2nd day while the weather is hot. Also give your maple and spruce a thorough watering in order to minimize any stress you may have caused.
Fine Gardening’s article Planting Under a Tree has a section on which trees can tolerate root disturbance
Hope this helps.