Based on the information provided by you, it appears that you do not have an HUF as on date. So it will be dificult to claim all the building expenses under HUF as your HUF does not have adequate funds/ capital. Again the Land is in your personal name and the building expenses would be done through HUF.
I would suggest not to unnecessarily complicate the process.
About the gift part, yes you can gift the income generated to your Grand Children even if the income is earned in your personal name.
Trust this clarifies your query.
Feel free to call / get back in case of further clarifications.
Rohit R Sharma
BCOM, ACA, LLB-GEN, CERT. FAFP.