What will happen if a small female mates with a larger male?

Question
Hi my female fox terrier who weights 5kg has tied with a 9kg japenese spitz. Will the female die? Will it require a C-section? Or is this size safe?

Also they have tied twice in a span of 2 weeks. What will happen? Will more babies be born? Or is the egg now full of sperm?

Answer
Is this a planned breeding? Because if it is not, I would get this dog spayed as soon as she comes out of heat.
The size difference isn't that great unless she is very small, and then a C-section costing hundreds of dollars may be necessary. I wouldn't risk it.

Every time a dog is bred they ovulate, which means more babies. That is why and how a dog can have a mixed litter from more than one male dog.

It isn't one egg, it's many each time they are bred.

Your safest course for her and you is to get her spayed now or as soon as she is out of heat.