Is it permissible for divorced parents to remarry so that the father's entry and exit from the house become permissible, without conjugal relations, and with each of them in a separate room?

If the intention is to stipulate the absence of marital intimacy in the marriage contract, then this is invalid and renders the marriage void, because it violates the primary purpose of the contract. However, if this condition is not explicitly stated in the contract, and the agreement is to forgo it later, there is no harm in that, because intimacy is a right for both spouses that can be waived.