Modern phone photos are large, and a handful of them will exceed most attachment limits. Shrinking them first is quicker than any workaround.
Attachments are encoded for transport, which makes them roughly a third larger in transit than they are on disk. A twenty four megabyte set of photos can be refused by a twenty five megabyte limit for that reason alone, so leave yourself real headroom.
Width is the lever that matters. Dropping a 4000 pixel photo to 1600 pixels removes most of the file size while still looking sharp on any screen the recipient is likely to use.
If the recipient needs the full resolution originals, say for printing, do not compress them. Send fewer at a time, or use a file transfer service and accept that this means uploading them somewhere.
Under about two megabytes each is comfortable, and several of those still fit within a typical limit.
On a screen, almost certainly not. In print at a large size, possibly.
No.