Bhutanese refugees like most Asians tend to be detailed in their explanation hoping to give an in depth description.You will find them talking in long sentences.Often it ends up being non specific for the provider who wants a yes/no answer.
Re: food, vegetables aside, their staple diet is mainly inclusive of carb enriched products like rice,potatoes,bread. So, it can be quite challenging to modify this since this is the only type of food they've been used to their entire life.However, they are very open to changes and if educated properly, they may heed to your advice.
What you need is a good interpreter by which I mean, someone who understands the cultural nuances and not just speak the language. Many Bhutanese patients have confided to me about how they don't understand some interpreters. Not all Bhutanese people speak Indian(Hindi) and often they are given Hindi interpreters. So, getting a Nepali interpreter would be more helpful.
Life for many Bhutanese refugees starts early on.They get married early,have kids early on .So in their 50s,most of them are already grannies/grandpas.So that psychologically may make them feel older.Also, in the rough terrains w/ hard labor,you tend to age faster.Things like using SPF sunscreen,anti aging tx are considered a luxury.
Most elderly Bhutanese refugees have never been to school.So, that answers why they wouldn't know how to sign.
They put a lot of faith into the provider's hands like 'you know it all and we're just lay men/women' and will generally not question your judgement.
Hope that was helpful!