grammar help needed pls

[tjj]

hello my dearest fellow beings,
good day to all of U.

Need some clarification on the following, please

1) prepositions
my mom teaches at a school in Oxford. (correct right ?)
can we say, my mom teaches in a school in Oxford?

2) prepositions:
when you invite people
a) into the house
b) to the house
which one is correct? or both are correct?

3) relative pronouns:
a1) that is the policewoman who stopped the car. OR
a2) that is the policewoman that stopped the car.
which is the correct one? And why?

b1) that is the bend which caused the accident? OR
b2) that is the bend that caused the accident?
which is the correct one? And why?

c) a vet is a man or woman who/whom can help injured or sick animals.
who or whom? if it is whom WHY?

d) wheat,maize and rice are important crops that keep billions alive.
can we use WHICH instead of that?

Many Thanks
Have a wonderful week.

with love
ted

[Tdol]

1 Yesa
2 It depends- if you are at work and invite them to come, then 'to' works, but if they have rung the doorbell, then invite them 'into' the house.
3 a/b You can use either
3c Who- subject
d Yes