Helvellyn is a bit short of an “all-dayer” if you do a single ascent but quite a tough “all-dayer” if you do it twice.
If your group is up to a double, then I’d recommend starting on the Thirlmere side (near #2 on the viewranger map) then go up Great Tongue but don’t take the bridleway as per the map, take the footpath to the right of the gill instead. It’s less boggy and you’re carrying anyway!
At Grisedale Tarn, head up Dollywaggon and over the summit ridge to Raise. Descent Sticks and then Seldon Seen. Back up via Kepple Cove. Back over summit ridge opposite way. Descend Birkside as per Viewranger map.
If they’re only up to a single, then from Glenridding side, go up Grisedale valley (reverse of the viewranger route) to Grisedale Tarn. Up Dollywaggon. Over summit ridge and down Sticks/Seldom Seen.