Lomas will marry the Coronation Street star at the Nunsmere Hall Hotel in Cheshire today (September 2).
However, his 90-year-old grandmother Greta McPhee has spoken of her disappointment at not getting an invite.
"I feel like a leper. I've never asked them for anything and I don't know what I've done wrong," she told The Sun.
Meanwhile, several cousins, two aunts and an uncle are said to not be present at the marriage ceremony, while the couple's cleaner has been invited.
The former Hollyoaks star's cousin Jason Primo said: "What hurts most is that he's not invited our nana. She's been in floods of tears.
"It gets my goat that their cleaner is invited but not us."
Coronation Street stars Shobna Gulati and Antony Cotton will be among the guests at the wedding this afternoon.
Marsh recently said that she was feeling "relaxed" about the ceremony.