It's not that much of a disadvantage because when the house was left to A and B as joint tenants the registrar will have entered a s. 40 restriction on the register. So A won't be able to sell over B's head, even if B is not in occupation.
I don't know if A's refusal to convey to A and B jointly would in itself justify a sale under s 14 TOLATA. It might also depend why the property was conveyed to A and B in the first place - was it to be a family home, are they two strangers who hate each other but C wanted to leave them a house in a will so that they could sell it later, etc? See the factors in s 15 TOLATA.