Would need more information for answer this. I don't think B can force A to probate a will. B can file a probate action in probate court as if there's no will. B would serve A with the action and then A would need to come forward with the will or else the estate will pass as if there's no will--everything would go 50-50 to A and B--assuming no other siblings or a surviving spouse. Does the purported will provide for a treatment other than a 50-50 split of everything between A and B? If A takes the position that he/she gets everything under the will and proceeds accordingly without probate (not sure that's even possible), and if B does not agree then B should file a probate action as if there's no will in order to get A to produce the will.
It would be far better for A and B to work together and try to avoid probate all together. And some of the assets are likely not subject to probate and there may be a simplified way to get the house and other assets in A and B's name other than probating the estate. The life insurance and possibly the bank account will pass to the beneficiaries, or, in case of the bank account to the JOWOS, if there is one. As for creditors, the executor or court appointed administrator would have to perform some amount of diligence to identify creditors and serve them with a notice to file a claim. A or B should probably do that anyway and try to settle with creditors unless, and I don't know the answer to this, the assets in the estate are exempt from creditors' claims. I've never looked at it, but if there's no surviving spouse with a right in a homestead, I suspect that a decedent's residual estate property is always subject to creditors' claims.