[Tref]

I submit that it is some sort of anagram. Your poor papa is trying to communicate something to you but he is afraid to come out and say it directly.

So, let's take the words, Remember, you are the youngest son and see what we have.

"Er, buy term heterogeneous yam"

or, "Merry Heterogeneous tube yam"

By combining the two options I have come to the answer. I think your papa is saying, albeit, hesitatingly, something about the purchase of dissimilar (tube) yams, perhaps, a lot of them, over a period of time. And to be merry about it.

I think that solves that.

Thank you. Thank you very much.