Need gaining advice for my husband

You might think he's eating a lot in one sitting. But, what matters most is total calories throughout the day. On a usual bulk i'm gulping down around 4k cals a day. I would recommend to use the IIFYM calculator to calculate his TDEE and increase cals by 300 every week until he starts to add some pounds. But, you won't be able to do this by just "eyeing" his food. If he doesn't record it...there really is no way of knowing what his daily calls and macros are looking like.