Have you contemplated buying a cheaper, but Refurbished Vitamix?
But in the case of Vitamix blenders, the process of reconditioning machines is a serious, formalized 17-step process, and these certified-reconditioned blenders are what Holly Hacker, director of direct sales and customer experience at Vitamix, calls “truly good as new.” These refurbished ...
The ‘real’ solution is seedless grapes.
Blending seeded grapes in itself isn’t any issue for the blender, it simply won’t care at all… however if you blend too long you will break through the seeds’ outer jelly layer & start to grate the seeds themselves, which will make the resulting purée bitter.
If they are going to blend hot soups, go with stainless. Glass can (and does!) crack due to the thermal issues. If they are religious about cooling their soups down to room temperature glass can be ok. But I've definitely had glass jars crack when blending hot soups. Tempered glass does not solve all problems.
I'm surprised your grand parents did not have a glass blender before; they were and are still very common.
Glass jars are safe; I've not heard of reported problems with them; and have been in use for many, many years.
They are made with tempered glass and should not break during normal usage.
Also have a look at blender with plastic jars; maybe that could ...
In short, no. You could blend pencils and pens with most modern blenders and there's no damage to the blender. Fruit seeds won't be a consideration except in use of the blended fruit. You might need to strain the output to remove bits of hull.