Need advice on this

Last week my dh only sibling got diagnosed with cancer of womb and is to get it removed. Just now were going through the testing stage of fertility clinic but he feels we should hold off as it won't be fair tryin for a baby when we know she won't be able to have anymore.(she already has 2perfect girls) We've been tryin over a 14month now and I've tried explaining if we stop tryin then that's it I can't do it again but he says I'm being selfish. Is it wrong that I think she should think herself lucky she's got 2beautiful girls over having none and can't have any?