Hello
Yellowing leaves could be lack of water or you may have the disease called black spot several of my roses of mine have some are more prone to others plus we have had a array of weathers just lately warm then cold sudden cold snaps so it could just that they should recover.
If you give the rose names i can have a look for you as i am a member of the RNRS. Here's some general advice below.
Rose Care Advice
Feeding and Mulching
To get the best from roses they need regular feeding. An old rose saying is 'a well fed rose is a healthy rose'. A clay soil will need the addition of a rose fertilizer twice a year, in March (after pruning) and after the first flush of flowers is over (usually late-June to July). Roses growing in a sandy or chalky soil will need feeding monthly from March to end-July - a small handful of rose fertilizer will suffice.
Roses growing in aloamy soil will benefit from feeding three or four times between March and the end of July. Mulching is a good practice: garden compost, leaf mould or well-rotted manure will keep the moisture in the gorund, but bark chippings are best avaoided.
Watering
Roses will tolerate a dry soil but thrive in a moist, well drained soil. If the ground is dry, water well occasionally. Little and often watering is best avaoided. Rose growers find watering in the morning or keeping the leaves dry reduces incidence of disease.
Pests and Diseases
Many pages have been written on keeping rose free of pests and diseases, but with good husbandry (proper feeding and watering) and choosing heathly varieties of roses they can be avoided. If diseases appear spray with a popietary fungicide.
If pests (aphids) are troublesome try wiping them off or use an insecticide such as derris which is due to banned from September 2009
Cheers
Brogusblue