There is no tzniut issue involved with your husband helping your father dress or undress, as needed.

If there is no readily available male alternative, you may help your father dress and undress.

You should make every effort not to look at or touch his genital area, when possible. Draping a cloth of some sort can help in these situations.

A similar answer applies regarding your mother-in-law. Your husband may help her dress and undress if no female alternative is available. He, too, should make every effort, to the extent possible, to preserve tzniut in the process.

Both of you may consider contacting an occupational therapist for advice about techniques available to make your parents more independent and to facilitate your helping them comfortably.

We wish them both a refuah shleimah, and wish both of you the strength to navigate this time together.