Mulch the entire length of the line of the spruces - it doesn't matter if they are not that close to each other. A long, continuous bed of mulch will be visually more appealing than round, individual 'tree circles'. And it will keep the weeds and other undesirables down in any open areas between the trees. Bring the mulch out about 3' from the trunks - the purpose of mulch, in addition to suppressing weeds, is to conserve soil moisture and the tree roots will extend well beyond the canopy dripline. Turf grasses and weeds will compete with the trees for water and soil nutrients so keeping them well away from the trees is beneficial. Just keep the mulch from touching the trunks.

Mulch will stop some weeds, but enable other ones. Usually, it seems to help keep weed populations reduced.

There is no reason to avoid touching tree trunks with mulch, as long as it is minimal, like an inch deep. In time, it could be increased slightly, but no real need.

The new National Champion Ponderosa Pine has about 4 feet to 5 feet of needle mulch against it's trunk that it put there itself slowly over time.

Part B to my earlier reply ...

It is possible to see a surge of weed or tree seedling germination after putting mulch down. If there is a surge due to seeds on the ground that you may not have seen, don't get discouraged with mulching. The practice is very worthwhile.