Because your husband is T2D, I advise waiting for others more informed about the special requirements for T2D to add their input before changing anything. My comments should be taken as suggestive until they do so.
You say the two of you ‘started the keto diet’ on April 25. That’s 2 weeks and a day ago. You don’t mention your ages, but whatever the two of you ate SAD for all those years and keto for 15 days. Don’t expect miracles and you won’t be disappointed. Did you just start eating keto, whatever you thought it is? It would be helpful to inform us what in addition to the plums, you eat on a typical day? Or did you go on a multi-day fast to burn out glucose and glycogen stores? If you did not do the fast to kick start ketosis, and if you have not kept daily carbs sub-20 grams consistently, it is quite possible that neither of you is in ketosis or in and out.
You mention your husband’s ketostix ‘readings’ have been negative. Does that mean no colour? If so, that does not mean he’s not in ketosis, just that he’s not dumping excess ketones via urine. If he says he feels great and has more energy, that’s good. But in his case, it’s very important to keep the carbs sub-20 grams consistently. If your readings indicate ketones in your urine, you are dumping excess, which is typical when starting out. Are you testing only once per day or multiple times? It’s probable when you are in/out of ketosis that you will get different readings throughout the day.
The fastest and easiest way to get into ketosis is a 3-4 day fast. It only hurts on the second day when carb hunger reaches its peak. If you can’t/won’t do the fast, eating your way to ketosis takes much longer. The ‘2 to 4 days’ you mention is unrealistic unless you do the fast.
Welcome and best wishes.