Learn English – Idiom criticizing a person who has unsolved problems but tries to give someone advice about them

Is there an idiom or expression that refers to a person who has some unsolved problems and tries to give some pieces of advice to, or guide, others for solving the same problems?

We Iranians have a proverb that literally means

“If a bald man were capable of curing baldness, he would cure himself first!”

This sarcastic proverb implies that “…while someone is incapable of solving his own problems, he is in no position to guide others on how to solve the same problems.”

Examples:

1. Suppose I have made many mistakes in my married life and now I'm in the midst of getting divorced; one day my colleague (person A), who is about to get married, asks my colleagues and me for some advice on how to have a successful married life. When I start giving my opinion, another colleague (person B) might turn and say to person A:

   "Why are you asking Soudabeh? If she really knew how to have a happy married life, she wouldn't be in this situation now; as that old proverb says "if a bald man could cure baldness, he would cure himself first!"

2. There is a country (A) in the region which has been fighting some terrorist groups for some years and has not been successful in destroying them; now its neighbor country (B) is facing the same problem. If country A's leaders try to guide country B's government on how to fight against those terrorists, country B's leader might say "You are not in a position to guide us! If you had been capable of solving this problem, you would have solved it in your own country, if a bald…"

I have found this idiom "physician, heal thyself". Can I use it as an equivalent to that Persian proverb? (Although it seems that it focuses on "defects" rather than the "problems".)

Notes:

• The bald man here refers to the one who has been involved with an
  inherited baldness or a permanent baldness due to a disease like a
  ringworm (fungal infection).

• We use this proverb when we are talking to/about our close friends
  or younger relatives, or to people for whom we don't care about them being
  offended hearing it (we rarely say it to a really bald person to
  prevent them taking it personally and getting upset). Also, this
  proverb is commonly used among politicians and opposing parties
  as a way of mocking each other for not being able to solve their own
  problems and yet trying to guide others on how to solve the same
  problems.

• Using this proverb doesn't mean that the speaker is accusing somebody
  but just implies that they are not in the position to give
  advice about the given problem(s).

Maybe this cartoon gives a better idea. (What is your first impression of that?) Are you ready to go to this dietician? 🙂

One might reply :"No, I won't. Because if he knew how to treat obesity, he would treat himself first!, as the idiom/ proverb says _____ ."

Actually, I'm looking for something that can be used in this sentence, too (as an equivalent for that Persian proverb).