You cannot force the company to accept your husband as a shareholder. Any share transfers, including through your will, are governed by the company’s articles of association and any shareholders’ agreement. For example, these might allow the company’s directors to block any transfer.
You should check what the articles and any shareholders agreement say and take legal advice. Your best option may well be to deal with this situation now — for example, by negotiating an agreement with your children — rather than risk creating a dispute after your death.