Am I obliged to perform the Hajj and sell my land or my car to achieve that, knowing that my income is limited and I am unable to build a house for my family?

Hajj is an immediate obligation upon the one who is able. If land or a car is essential for your needs and the needs of your children, you are not required to sell it for Hajj. If the car is more than what is needed and its purpose can be fulfilled with a less expensive one, then it must be sold and the surplus used for Hajj. As for land, if you need it for housing or rent, you are not required to sell it. However, if it is in excess of your basic needs and intended for future construction, then it must be sold and its price used for Hajj. The ability to perform Hajj is considered to exist when one has surplus beyond essential needs such as housing, books of knowledge, merchandise whose profit would be affected, debt repayment, and family expenses. However, if there is a surplus from housing or a servant that exceeds the need, and it is possible to sell it and purchase what suffices for the need, with enough left over for Hajj, then that becomes obligatory. Hajj is a cause for an abundance of sustenance and its blessings.