Hi Karin. My t. grans stay around 74 in my apartment, but that's really pushing the limit on being too warm. If there were any other stress factors for them right now I would be worried.
Keep them below 70 if possible. And I assure you, they don't want it to be warmer. If you could keep them at 50 degrees they would love you forever. Keep them as cool as you can. A basement is a great place, if you have one.