SLT compatibility with old Minolta fit Sigma lenses

Sorry if this has been asked and answered before. I am currently a nikon user but used to use Minolta Dynax film cameras. My wife Barbara still has her Minolta 500si and we have a mixture of Minolta & Sigma lenses from that same period.

Barbara is interested in possibly buying a Sony DSLR to use with those lenses and I was looking for a Sony DSLR model comparable to her 500si (mid range consumer).

It looks as though the entire DSLR range has now been suplanted by SLT models, and I think i read somewhere that older Sigma lenses do not work well or are not compatible with SLT cameras. The lenses in question are a slow standard zoom and a 70-300 APO zoom.

So would these be usable at all and if so with what caveats. (I realise of course that they are not optimised for digital and there will be more vignetting and possibly some loss of contrast)

Thanks in advance for any advice offered.

Regards

John