where can I find instructions to hook these up to the unit?

What unit you're connecting the receiver with? What is the model? So we can send you wiring diagram, or you can refer to the manual of the unit, there should be wiring diagrams.

Are these ok to use outside where it might get rained on?

Switches must not be directly exposed to rain. However, indirect exposure (e.g., under eaves/overhangs) is acceptable as long as physical protection from precipitation is provided.

Can wireless receiver frequency be changed when using more than 1 receiver on 2 separate doors that are close to each other.

Hi, If you use more than 1 receiver on 2 doors that are close together but independent of each other, they are in the same frequency band, but the exact frequency of each receiver is still different.

Can you have more than two push switches?

Yes，you can pair more than 2 switches with the receiver。

Is the Olidesmart M-510 Handicapped Push Switch weather resistant ? Can the switch be outside ?

The working temperature of the handicap switch is -42C° to 45C°; and the waterproof rating of the push button switch is not high, it is recommended to make a cover above the switch if used outside.

I just want to order four buttons at 89 no receivers thank you

Yes, I saw your order, will ship it soon.