I'd ask what kind of ponies they plan to put 4 of, 4 shetlands or small native types unshod is one thing, or perhaps something bigger with health problems eg laminitis or recovering from lameness that needs restricted grazing or space, but if they're talking any bigger than 12'2 hands I wouldn't allow it on 2.5 acres except as a seasonal grazing lease ie March-October only and they remove them for the winter.
Wish you lived nearer me, I'd use it for 2 max 14'2 Highlands on a long term basis, or 3 to 4 in summer to keep them trim and the grass tight, then run sheep after them and rest it til spring. Wish I could do that with my own land and it wouldn't be over my wellies in muck around the gates, water trough, feeding areas and storm shelter spots!