What is the ruling on purchasing a house through the aforementioned banks with fixed interest, knowing that the company will pay 70% of the interest?

It is permissible to purchase a house through a bank if the bank owns the house before selling it to the employee by way of Murabaha (at a higher, installment-based price). And if the company contributes 70% of the bank's profit. There is no harm in transferring the salary to the bank (even if it is interest-based) as a means of safeguarding the bank's right, and the remainder of the salary should be withdrawn immediately after the installment is deducted.