First question
The scenario you’ve described involves borrowing cash from multiple persons and then depositing the total amount in a bank savings account for a specific purpose. From an income tax perspective, this situation might be subject to scrutiny, and certain provisions of the Income Tax Act may be relevant. Your question is about section 68 & 69 but you should be more asking for 269SS & 269ST. SOme of the important sections explained here-

Section 68: Unexplained Cash Credits
Section 68 of the Income Tax Act deals with unexplained cash credits. If any sum is found credited in the books of the taxpayer for which the taxpayer offers no explanation about the nature and source thereof, or the explanation offered by the taxpayer is not, in the opinion of the Assessing Officer, satisfactory, the sum may be charged to income tax as income of the taxpayer of that previous year. Hence you may keep a full record of the transactions with Name , PAN etc of the person from whom cash is accepted. BUT IF the explanation offered by the taxpayer is not, in the opinion of the Assessing Officer, satisfactory, the sum may be charged to income tax as income. But if you can provide a satisfactory explanation with a record then you are not covered in 68. 

Section 69: Unexplained Investments
Section 69 of the Income Tax Act deals with unexplained investments. If, in any financial year, a taxpayer is found to be the owner of any money, bullion, jewelry, or other valuable article and such assets are not recorded in the books of accounts, and the taxpayer offers no explanation about the nature and source of acquisition of these assets or the explanation is not, in the opinion of the Assessing Officer, satisfactory, the value of the assets may be deemed to be the income of the taxpayer for that year.But if you can provide a satisfactory explanation with a record then you are not covered in 69. 

Section 269SS: Mode of Taking or Accepting Certain Loans and Deposits
Section 269SS deals with the mode of taking or accepting certain loans and deposits. As per this section, no person shall take or accept from any other person any loan or deposit otherwise than by an account payee cheque or an account payee bank draft if the amount of such loan or deposit is Rs. 20,000 or more. If a loan is taken or accepted in contravention of this section, the borrower is liable to pay, by way of penalty, a sum equal to the amount of the loan or deposit. In your case, cash of 19000/- is accepted from 50 different people. Hence it seems that this section is not violated but you need to keep a record and be ready to explain when asked by the income tax department.

Section 269T: Mode of Repayment of Certain Loans or Deposits
Section 269T specifies the mode of repayment of certain loans or deposits. According to this section, no branch of a banking company or a co-operative bank and no other company or cooperative society and no firm or other person shall repay any loan or deposit made with it otherwise than by an account payee cheque or an account payee bank draft if the amount of the loan or deposit is Rs. 20,000 or more. Keep it noted.

Section 269ST: Mode of Receipts in Certain Transactions
Now coming to this crucial Section for your case, 269ST , provides
No person shall receive an amount of two lakh rupees or more—
(a) in aggregate from a person in a day; or
(b) in respect of a single transaction; or
(c) in respect of transactions relating to one event or occasion from a person,
otherwise than by an account payee cheque or an account payee bank draft or use of electronic clearing system through a bank account [or through such other electronic mode as may be prescribed].
If a person receives a sum in contravention of these provisions, he/she shall be liable to pay a penalty equivalent to the amount of such receipt.
In your case , cash receipts is from different persons, dates are not specified in question -you may check it, aggregate value is also above 200000/- , Hence if this is for a single transaction then you are covered, and a penalty may be imposed. A single purpose that’s son’s visa may be considered as a single transaction.
If a person receives a sum in contravention of these provisions, he/she shall be liable to pay a penalty equivalent to the amount of such receipt.

Question TWO
As per section 3 of THE BENAMI TRANSACTIONS (PROHIBITION) ACT, 1988, 
(1) No person shall enter into any benami transaction.

(2) Nothing in sub-section (1) shall apply to the purchase of property by any person in the name
of his wife or unmarried daughter and it shall be presumed, unless the contrary is proved, that the
said property had been purchased for the benefit of the wife of the unmarried daughter.

(3) Whoever enters into any benami transaction shall be punishable with imprisonment for a term
which may extend to three years or with fine or with both.

(4) Notwithstanding anything contained in the Code of Criminal Procedure, 1973, an offence
under this section shall be non-cognizable and bailable.
IN your question, if son is buying property in his mother’s name, Benami Act, will be attracted. Buying property and registering it in the sole name of mother or father will attract benami ACT.
The Individual (son/daughter) paying consideration may buy it in the Joint names of self and mother/father and with his known sources to ensure that the Benami Act is not violated.